CHAPTER VI

RESULTS OF THE KITE-FLIGHTS AT BLUE HILL--FUTURE WORK

Kites possess several advantages over other methods of exploring the air up to heights of at least 12,000 feet whenever there is wind, but their chief merit is, that with them the true conditions of the air may be ascertained. The disadvantages of other methods of exploring the air, as compared with kites, are these:

1. =Mountains= not only affect by contact the adjacent air, but by deflecting the air-currents cause mixture and ascent, which give conditions differing widely from those of the free air.

2. =Free Balloons= are more or less surrounded by heated or stagnant air, because they drift with the wind, and on account of the sluggishness of the thermometers, the temperatures observed at a given height in a balloon are generally higher during the ascent, _i.e._ when passing from warm to cold air, than during the descent, when the conditions are reversed. Again, it is not possible to study the progressive changes in the atmospheric conditions at one place, because observations in a drifting balloon are not comparable with simultaneous ones made at a station on the ground below. With kites, however, the possibility of making frequent and nearly vertical ascents and descents permits observations to be obtained almost simultaneously in superincumbent strata of air. The height of the kite can usually be determined with an accuracy not attainable by the barometer in a balloon.

3. =Captive Balloons=, although constructed so as not to be driven down by wind, cannot rise nearly so high as kites on account of the weight and resistance of the cable necessary to control them, and even the German kite-balloon, on account of its large surface, would hardly withstand the strong winds in which kites can fly.

4. =The Cost= of installing and operating either mountain stations or balloons is much greater than for kites.

The exploration of the lower two miles of air with kites flown from Blue Hill is no doubt the most complete ever made at one place. Nearly two hundred records have been obtained in all kinds of weather conditions, and the progressive attainment of greater and greater heights is shown in the table in the preceding chapter. The records from the flights have been discussed by Mr. Clayton; those until February 1897, with the Blue Hill Observations, in Vol. xlii., Part I., of the _Annals of the Astronomical Observatory of Harvard College_, and later records in two _Bulletins_ of the Blue Hill Observatory, in which the changes of temperature and humidity with height, and their relation to the positions of cyclones and anti-cyclones, are investigated. The use of kites for weather predicting, as was said, has been tried by the United States Weather Bureau, but it is certain that further studies, such as have been made on Blue Hill, are necessary before the sequence of the conditions at the earth's surface to the phenomena observed in the upper air is definitely known, so that the latter can be utilized in forecasting.

Some of the deductions from the observations with kites at Blue Hill follow. Plate VIII. is a facsimile of the record of the baro-thermo-hygrograph during two flights on October 8, 1896, when for the first time the height of a mile and a half was attained. The record-sheet, it may be said, is wrapped around a cylinder that turns on its axis in twelve hours, and the curved lines in each of the three horizontal sections divide them into quarter hours. The lower section contains the trace of the barometer, the horizontal lines being the heights in metres and feet that correspond to the barometric pressure with a temperature of 32∞ Fahrenheit; in the middle section is the trace of the hygrometer on a scale of relative humidity in percentages, and in the upper section is the trace of the thermometer on a scale of temperatures in Fahrenheit and Centigrade degrees. It will be observed that the record of the barometer is reversed, _i.e._ the trace rises for falling pressure, and in the second flight when the unexpected height of 8697 feet above Blue Hill was reached, the limit of the altitude scale was exceeded.

In order to study the changes of these elements with height during the higher flight, in Plate IX., Figs. 4 and 5, the temperature and humidity of the automatic record are plotted as abscissÊ, with the heights above sea-level in metres as ordinates. For those not familiar with this unit of length, it may be said that 100 metres are about 330 feet, and that 1600 metres equal one mile approximately. When the meteorograph was ascending, dots indicate the recorded temperatures and humidities, which are each connected respectively by continuous lines; when the meteorograph was descending, crosses indicate the observations, which are connected by broken lines. Lines inclining upwards to the left indicate decreasing temperature and humidity with increase of height, and lines inclining to the right increasing temperature and humidity with height. The straight dotted lines show the adiabatic decrease of temperature for ascending dry air. The ascent was made during the warmest part of the day, and the descent for the most part after sunset. The two branches of the temperature-lines typify the temperature change with height which usually occurs in fair weather during the day and the night respectively. The continuous line, representing the day observations, shows a uniform fall of temperature at the adiabatic rate to the cloud level. During the night, the lower part of the broken line bends decidedly to the left, showing a body of relatively cold air near the ground, caused by radiation. There is a rise of temperature with increasing altitude above the ground up to a certain height, and afterwards a comparatively uniform fall as high as the clouds, if they exist; but the rate of fall with increasing altitude, shown by the upper part of the diagram, is slower at night than during the day. It appears that the diurnal change of temperature is very small at great altitudes, compared with the change near the earth's surface. The relative humidity (Fig. 5) up to 2000 metres varies inversely with the temperature, and in the present case there was only a slight change in the direction of the wind (Fig. 6).

=Diurnal Changes of Temperature at Different Altitudes.=--The curve representing the diurnal change in the air at some distance above the ground is probably similar to one representing the change near the ground, except that its amplitude is less. If this be true, then the diurnal rate of fall for a given time at any two levels will be proportional to the daily ranges of temperature at the two levels. It is impossible in practice to keep a kite at exactly the same level for twenty-four hours; hence the daily ranges for the different levels must be found by comparing the rates of rise or fall of temperature for given times with the rates found from records near the ground, made simultaneously with those above. In Plate IX., Fig. 1, the results for six stations, _i.e._ the kite at 1000 and 500 metres, the Eiffel Tower in Paris (300 metres), the summit of Blue Hill, its base, and the valley (200, 50, and 15 metres respectively), are connected, and a smooth curve is drawn through them. The curve passes approximately through every one of the observed and the computed ranges, except the one at the summit of Blue Hill, which is too great. This evidently is because insolation and radiation, acting through the soil of the hill, heat and cool the air to a greater extent than the free air is heated and cooled at the same altitude, and this must be true at every mountain station. The smoothed curve passes also very slightly to the left of the data for the Eiffel Tower, indicating that the range there is about 1∞ greater than the true range on account of the heating and cooling of the Tower. From this it appears that the diurnal range of temperature diminishes rapidly with increasing altitude in the free air, and almost disappears in the average at a height of 1000 metres.

The records of the anemometer show that, as a rule, the wind increases steadily as the kites rise, but the increase is greatest between Boston and the top of Blue Hill, due probably to the retarding of the lower winds by contact with the ground. The results are plotted in Plate IX., Fig. 3, together with the mean wind velocity on Blue Hill (209 metres), and the velocity on a tower in Boston (60 metres). Single records of the kite-anemometer differ much, for sometimes the wind velocity diminished with altitude, and at other times it increased so rapidly that the kites were unable to rise higher. On several occasions when the kites passed from one current into another, having a different direction and a different temperature, the wind suddenly increased, and was stronger between the two currents than above or below that plane.

=Diurnal Changes of Humidity at Different Altitudes.=--It is found that as night approaches the humidity at the altitude of 1000 metres diminishes, while at the earth it increases. This agrees with the evidence furnished by the cumulus clouds that form during the day between 1000 and 2000 metres, and disappear at night, thus visibly indicating an increase of humidity by day and a decrease by night. If the trend of the humidity-curve at a height of 1000 metres is assumed to be the reverse of its trend at the ground, then the results from the kite-meteorograph show the minimum humidity to be at the coldest and the maximum humidity at the warmest part of the day. The mean daily ranges for different altitudes are plotted in Plate IX., Fig. 2. The part of the curve at the left of the zero line shows the range at different altitudes, with the minimum humidity near the warmest time of day, while the part at the right of the zero shows the ranges at different altitudes, with the minimum humidity at the coldest time of day.

=Types of Change of Temperature with Altitude.=--When the records of temperature and humidity made aloft by the kite-meteorograph and at the stations near the ground are plotted in relation to altitude, they are found to be easily divisible into a few types. In Plate X., Type 1 represents the decrease of temperature on most fair days from the ground to altitudes of a mile or more, when no clouds are met. The continuous line, plotted from the records of the ascent, represents the day conditions, and the broken line, plotted from the records of the descent, represents the night conditions. This curve shows that with increasing altitude the temperature falls uniformly during the day and approximately at the adiabatic rate represented by the dotted lines. The fall of temperature with increasing altitude during the night is slower than during the day, and in fact, from the earth's surface to an altitude of a few hundred metres, there is often a rise of temperature with height, so that the air at altitudes of from 300 to 500 metres may be considerably warmer than it is at the ground. This was shown in the descent on October 8, 1896, and is found in Type 3.

When clouds are traversed during the flight, the temperature curve assumes the form of Type 2. The continuous curve is plotted from the records of an ascent; the broken curve from the records of the descent, both occurring in the day-time. The temperature falls at the adiabatic rate in unsaturated air till the base of the cumulus cloud is reached. It falls at a slower rate in the cloud, the rate probably being that computed by physicists as the adiabatic rate for air in which condensation is taking place. Above the clouds, the fall of temperature appears to be very slow.

Type 3 is a condition which persists throughout the day and night, and it resembles the night form of Type 1. The temperature rises very rapidly for a short distance above the ground and then falls, with increase of height, somewhat slower than the adiabatic rate. The rise of temperature near the ground with increasing height is more marked after sunset than during the day-time.

Type 4 was illustrated by the ascent of October 8. This distribution of temperature is caused by a warmer current overflowing colder air, which is very commonly found at low altitudes in the atmosphere and probably exists usually at some altitude, great or small. Recent observations indicate that this type represents the normal condition of the atmosphere in all sorts of weather. Frequently there are two or more sudden rises of temperature at different heights, so that the plotted data resemble inverted stair-steps. During the day there is a decrease of temperature at the adiabatic rate (1∞∑8 in 100 metres) from the ground to the height of several hundred metres, then a sudden rise of temperature in the next one or two hundred metres, and above this a slow fall of temperature with increasing altitude, usually much less than the adiabatic rate. Generally, clouds are found near the plane of meeting of the warm and cold current.

The reverse of Type 4, that is, a sudden fall of temperature, due to a colder current overlying a warmer one, is probably impossible, because the colder air, on account of its greater weight, would immediately begin to sink and the warmer air would rise. This should cause a fall of temperature at the adiabatic rate from the ground to the top of the colder current, and is probably the origin of the "cold wave" shown in Type 5. Both the continuous and broken curves (representing an ascent and a descent) show a fall of temperature at the adiabatic rate of unsaturated air, from about 500 metres to the highest point reached. Up to 500 metres the decrease of temperature is more rapid than the adiabatic rate, due to the rapid moving in of colder air above, whereby air rising from the ground is cooled by contact as well as by its expansion, and also because the air is heated more than usual by contact with the ground, which under these conditions is abnormally warmer. This is the special characteristic of the "cold wave" type of curve during the day hours. The night form of Type 5, notwithstanding the excessive radiation from the ground through the dry air, shows a rapid decrease of temperature with increase of altitude from the ground upward.

Type 6 shows a less common, but an interesting form, of vertical distribution of temperature, in which the temperature is about the same from 400 metres to 1400 metres or more. Up to 400 metres there is a fall of temperature with increasing altitude during the day, and a rise with increasing altitude at night. These last conditions can be readily traced to the effects of insolation and radiation near the ground. In the morning, if the temperature of the air be the same from the ground up to 1000 metres or more, the heating of the ground by the sun will cause ascending currents, until the warmest part of the day. This air, cooling by expansion at the adiabatic rate, will rise to about 440 metres before it assumes the mean temperature of the upper air column. At night cooling takes place next the ground by radiation and is gradually transferred upward a few hundred metres by conduction, thus producing an increasing temperature with increasing altitude, until sunrise. As a result of the conditions described, it is evident that on certain days the diurnal range of temperature is but little felt above 500 metres.

=Types of Change of Relative Humidity with Altitude.=--As in the temperature types, the continuous lines represent the records of the ascent, and the broken lines the records of the descent, generally under changing conditions. Lines inclining upward to the left show a decreasing humidity, and to the right an increasing humidity.

Type 1 may be called a normal type of curve when there are clouds. A variation of this type was met with in the ascent on October 8, 1896, and it differed from that now illustrated in indicating in its upper part a fall of humidity rather than a rise. These two types can be taken as the normal change of humidity with change of altitude in cloudy or partly cloudy weather. The humidity increases steadily to the base of the cloud, then there is complete saturation in the cloud, and above it is a sudden fall of humidity, on entering the dry air above the cloud, into which the ascending currents from the ground have not penetrated.

Type 3 is a clear-weather form of curve in which the humidity increases until a certain altitude is reached, probably at the upper limits of the currents rising from the ground. Above this altitude the humidity decreases rapidly.

Type 5 is also a clear-weather form and accompanies the "cold wave" type of temperature, also numbered 5. The very dry descending air mingles with air rendered damp by ascent, and the result is a nearly uniform relative humidity at different altitudes, although the absolute humidity diminishes on account of decreasing pressure and temperature. In Type 6 both the relative and the absolute humidity decrease rapidly, this type coinciding with the temperature, Type 6.

During the week of September 5 to 11, 1897, kite-flights were made daily on Blue Hill. Twice the kites were maintained in the air, and continuous records were obtained during most of twenty-four hours. These records furnish an example of the small diurnal changes of temperature in the free air at short distances above the ground, which were deduced from the average changes at different hours and at different heights. From 2 p.m. of the fifth to 2 p.m. of the sixth, the altitude of the self-recording instruments varied between 500 and 1000 metres above sea-level, averaging about 700 metres and varying little from this height during much of the night. The times when the kite-meteorograph crossed the 700-metre level in ascending and descending were determined from its barograph trace, and the synchronous temperatures and humidities were read from the records of its thermograph and hygrograph. The results have been plotted in Plate XI., Figs. 1 and 2, together with the temperatures recorded simultaneously at the summit and valley stations of the Observatory and the humidities at the summit. Fig. 1 shows that the diurnal variation of temperature, well marked at the lower levels, is very slight or has entirely disappeared at 700 metres. Fig. 2 shows that the course of the relative humidity at 700 metres is exactly opposite in phase to that recorded at lower levels, for at 700 metres the minimum humidity was recorded at night and the maximum during the day, while the opposite conditions prevailed on the hill. Repeated kite-flights indicate that these are the normal conditions at the two levels.

In Plate XI., Fig. 3, is plotted a curve from the hourly readings of the thermograph at the Blue Hill valley station (fifteen metres) during the week, and also a curve connecting temperatures recorded by the kite-meteorograph once or twice each day during the same week at a level of 500 metres, obtained in the way described or computed from the adiabatic change. All the night records show that it was decidedly warmer at the height of 500 metres during the night than it was at the ground, except during the cool wave on the seventh and eighth. Furthermore, the curves in Fig. 3 indicate a control of the surface temperatures during the day by those above. For instance, on the seventh there was a distinct flattening of the day curve, evidently because, as the temperature on the ground rose 10∞ above that at 500 metres, the air was in unstable equilibrium, and colder air descended to take the place of the surface air so that its temperature could rise no higher. On the tenth, the temperature at 500 metres was considerably greater than the mean of the day at the ground, and the air at the ground did not acquire the unstable condition in any volume until the warmest part of the day, so that the diurnal curve at the lower station forms a sharp peak.

Since there appears to be no appreciable diurnal period in the temperature at and above 500 metres, a better comparison of the relative changes aloft and below during the passage of warm and cold waves is obtained by smoothing out the diurnal period below. This has been done in Plate XI., Fig. 4, with the data given by the kites at 500 and 1000 metres plotted in curves, which it was necessary to complete by extrapolation. It is seen that there is a much greater range in the temperature from the crest of a warm to the crest of a cold wave at a height of 500 metres than at the ground. At 1000 metres the range appears to be slightly greater than at 500 metres, and the crests of the warm and cold waves occur successively earlier than they do at the ground. On the approach, and until the passage of the crest of the cold wave the air is colder aloft than at the ground, the difference being apparently that of the adiabatic cooling of ascending air. After the passage of the crest of the cold wave, the temperature aloft rises much more rapidly than at the ground, and at the crest of the warm wave the air at 500 metres is some 10∞ warmer than the mean daily temperature at the ground. In many kite-flights the difference was found to be even greater than this. Taking the mean temperature of twenty-four-hours, it is seen that the average temperature at the ground during a week or more is about the same as it is at 500 metres. Fig. 5 shows the change in the vertical distribution of temperature during the oncoming of the warm wave on the eighth and early morning of the ninth, as determined by four ascents, culminating at 11 a.m., 9 p.m., 11 p.m., and 4 a.m. The lines of 59∞, 62∞, 65∞, and 68∞ show that there was a gradual rise of temperature aloft, which extended downwards to 200 metres, or to the top of Blue Hill. Clouds formed at the level of lowest temperature, and these sank also until they covered the top of the hill.

Plate XII. is a facsimile of the meteorogram during the kite-flight of October 15, 1897, the lower part showing the trace of the barometer on a scale of heights in metres, the middle section the trace of the hygrometer, and the upper one the trace of the thermometer on a scale of Centigrade degrees. The temperature followed the normal change, which is as follows: during the day, up to a certain height, which varies under different conditions, there is a decrease nearly at the adiabatic rate of 1∞∑8 F. per hundred metres. Above that height the air suddenly becomes warmer, and then cools with ascent at a rate somewhat less than the adiabatic rate. During the night there is a marked inversion of temperature between the ground and 200 or 300 metres.

Higher than this, the temperature decreases at a fairly uniform rate, but more slowly than the adiabatic rate. Although no clouds were visible, yet the relative humidity increased greatly, both during the ascent and descent, near 1500 and 2700 metres, these being about the heights at which cumulus and alto-cumulus clouds usually form.

During September 1898 four kite-flights were made on four successive days when an anti-cyclone and a cyclone passed nearly over Blue Hill. This is a rare occurrence, and the mechanism of these phenomena was accordingly studied by Mr. Clayton, some of whose deductions will now be given, illustrated by Plate XIII. Figs. 1 and 2 give the temperature plotted according to height on September 21 in the anti-cyclone, and on September 22, when the barometric pressure was falling, the full lines, as in previous diagrams, indicating observations during the ascents, and the broken lines observations during the descents. It is seen that from the ground the lines all incline upward to the left, indicating a fall of temperature, to a certain height when the lines bend to the right sharply, showing a sudden rise of temperature. Above this, the temperature again falls, but more slowly than at lower levels. The general prevalence of this phenomenon was noted by Welsh in his balloon ascents in England in 1854, and the high kite-flights at Blue Hill show it to be very frequent below 2000 metres. The plane of increased temperature usually determines the height of the tops of cumulus and strato-cumulus clouds. Above 2000 metres other sudden rises of temperature are found during the highest kite-flights.

Figs. 3 to 6 show the changes in the various elements during the four days at some of the following levels, viz. near sea-level, 200, 1000, 2000, and 3000 metres. Fig. 3 shows the changes in the barometer at the four levels, from which it is evident that the fall of pressure was greatest near sea-level.

Fig. 4 shows temperature changes at the different levels, and indicates that the changes were of the same nature up to 3000 metres. The greatest non-diurnal range of temperature is seen to be at 1000 metres, and it diminishes both at higher and at lower levels.

Fig. 5 shows changes in relative humidity at 200, 1000, and 2000 metres. The curves show that the greatest range of humidity was at 2000 metres. There the relative humidity rose from almost zero, in the anti-cyclone on the twenty-first, to saturation at the same level in the cyclone. At 200 metres the change is similar to that at 2000, but is less in amount. At 1000 metres the relative humidity fell until the twenty-second, but then rose rapidly, showing the very dry air at 2000 metres on the twenty-first had descended as low as 1000 metres on the twenty-second.

Fig. 6 gives the change in wind velocity at the different levels. There was an increase of wind at all the levels from the time of the passage of the anti-cyclone to the passage of the cyclone. The minimum of wind at 200 metres was in the anti-cyclone, with a secondary minimum during the passage of the centre of the cyclone.

Figs. 7 to 10 show the changes in height from day to day of the equal conditions at the different levels. Fig. 7 shows the change in level of the isobars, which, although very small, is largest at the lower levels. The light broken lines in Fig. 7 and subsequent figures indicate the axes of the anti-cyclone and cyclone. That the axis of the cyclone was inclined backward, and that the high pressure occurred later at high than at low levels, was confirmed by the wind observations on the twenty-first.

Fig. 8 shows the heights at which the same temperatures were found on successive days. Since the isotherms rose until the twenty-third, the temperature of the air up to 3000 metres was higher on the day of the cyclone than on the day of the anti-cyclone. Previous high flights indicate that this is the normal condition in the moving cyclones and anti-cyclones of the eastern United States. As the light broken lines represent the axes of the anti-cyclone and cyclone up to 3000 metres, it is seen that at this level the temperature at the place of maximum pressure is probably higher than at the place of minimum pressure, although this is not true for a vertical column of air above the earth.

Fig. 9 gives the positions of equal humidities on successive days, saturated and cloudy areas being indicated by crossed shading, and less humidity by single ruling. From the laws of thermo-dynamics the unshaded curves should represent descending currents, and the shaded portions ascending ones. In the first case, increased warmth and a lower relative humidity are produced in the descent to a lower altitude; in the last case, cooling, increasing relative humidity, and condensation are produced by expansion in the ascent to a higher altitude. Consequently, two regions of descending air are indicated, one in the centre of the anti-cyclone, the other in the centre of the cyclone.

Fig. 10 shows the change in height of the lines of equal wind velocity. With ascending currents and precipitation, high wind velocities were found at low levels, because of increased barometric gradient, while with the descending currents in the anti-cyclone and centre of the cyclone, the high velocities were found only at great altitudes. The study of these data indicate that the cyclonic and anti-cyclonic circulations observed in this latitude do not embrace any air-movements at greater altitudes than 2000 metres, except in front of the cyclone, when the air appears to be carried upward to a great height. Above 2000 metres there are probably other weak cyclones and anti-cyclones, or secondary ones, with their centres at different places from those at the earth's surface and producing a different circulation of wind. The observations of the cirrus clouds at Blue Hill indicate that at their level exists a cyclonic circulation above the anti-cyclone apparent at the earth's surface. The shallowness of our anti-cyclones would be inferred from the great differences in speed of the general atmospheric drift, for since the velocity of the general drift from the west is more than thirty times greater at 10,000 metres than it is at 200 metres, a circulation of great depth could not endure long. Cyclones and anti-cyclones appear to be but secondary phenomena in the great waves of warm and cold air which sweep across the United States from periodic causes.

The origin of cyclones and anti-cyclones is perhaps the most important problem remaining for meteorological study. The theory that they are produced by differences of temperature in adjacent masses of air, or, as it is called, the convectional theory of the American meteorologists, Espy and Ferrel, is opposed by the observations on mountains in Europe which were collected by Dr. Hann of Vienna. If the question can be solved by the use of kites, as seems to be foreshadowed by the results just stated, another foundation-stone will be laid in the science of meteorology and the status of the kite established as an instrument of research. The kite fails when there is little or no wind at the ground, but it seems possible in such cases to lift the kite into the upper air, where there usually is wind, by attaching it to a small balloon that, after the kite can support itself, shall be detached automatically. While the height to which kites can rise is limited, and the limit is probably being approached, judging from the less gain of altitude in recent flights, yet it seems reasonable to expect that, with favourable conditions, a height of at least three miles will be reached.

Besides lifting the meteorological instruments described, kites can carry apparatus for other investigations in the free air, such as the measurement of atmospheric electricity, and the collection of samples of air, to be examined for cosmic dust and bacteria. Cameras have been lifted by kites, as already said, and for the purpose of photographing the upper surfaces of clouds there is being constructed for the Blue Hill Observatory a very light automatic camera, similar in principle to M. Cailletet's apparatus for photographing the ground from a balloon.

The use of the kite as an aeroplane can only be alluded to in this book, and it may be sufficient to say that if a motor attached to a kite can, by wings or screws, propel it against the wind, the sustaining string is unnecessary, and we shall have the flying machine which Professor Langley tells us will soon be realized. The surface of our globe has been tolerably well explored; the exploration of the atmosphere by balloons and kites will continue to make great progress during the last year of the century, and at the end of the twentieth century we may confidently expect that as the seas now are a medium for transportation, so the ocean of air will have been brought likewise into man's domain.

INDEX

A

Abercromby (R.), classification of clouds, 42 Academy of Sciences, French, 18, 72-3 Academy of Sciences, Russian, balloon ascent, 72 Accademia del Cimento, 14 Actinometer, ViollÈ's, 115 Adiabatic rate of change of temperature, 29 Aeronautical Conference at Chicago, 125 ---- Conference at Strassburg, 97, 110 ---- Committee; International, 108 _AÈrophile_ balloons, 102, 104 Aerostatic Commission, French, 111 Air, collection and analysis of, 70, 73, 75, 82, 112 ---- weight of, 16 Aitken (J.), dust particles, 39 Alhazen (B. A.), height of atmosphere, 12 Altitudes, comparative, 20 AndrÈe (S. A.), balloon voyage to North Pole, 90 Anti-cyclones, 59, 170 Aratus, _Diosemeia_, 11 Archibald (D.), kites for meteorological observations, 122 Archytas, supposed inventor of kite, 117 Aristotle, 10, 11, 15 Assmann (R.), 86, 94, 108 Atmosphere, composition of, 24 ---- energy of upper portion, 58 ---- extent of, 28 ---- methods of exploring same, 35 _et seq._, 145 ---- moisture of, 34 ---- origin of, 23 ---- phenomena showing height of, 26 ---- Pliny on, 9 ---- temperature of, 28 Atmospheric circulation in cyclones and anti-cyclones, 60 ---- electricity, 70, 76, 121, 141

B

Balloon ascents, international, 108 _et seq._ ---- crossing the Atlantic by, 92 ---- invention of hot-air, 19 ---- kite, 94 Balloons, 19, 20, 21, 37, 68, _et seq._ ---- captive, 76, 93, 146 ---- changes of temperature observed in, 71, 73, 75, 77, 84, 88, 90 ---- changing the direction of, 93 _Ballons-sondes_, 98 _et seq._ Barometer, 15, 16, 85, 113 Baro-thermograph of Richard, 102 Barral, balloon ascent, 73, 84 Batavia, Java, international cloud measurements, 65 Batut (A.), photography from kites, 123 Berson (A.), balloon ascents, 81, 87 _et seq._ Bert (P.), respiration of oxygen, 82 BesanÁon (G.), 98, 99, 101, 104 Bezold (W. von), wave-cloud, 40 Biot (J. B.), balloon ascent, 73 Birt (W. R.), kite at Kew Observatory, 122 Bixio, balloon ascent, 73, 84 Blanc, Mont, 20, 21 Blanchard, balloon ascent with Jeffries, 70, 71 Blue Hill Observatory, 47, 51, 53, 64, 108, 126 _et seq._ Bonaparte (Prince Roland), patron of aeronautics, 112 Bonpland (A.), ascent in Andes, 20 Bonvallet (L.), exploring balloons, 99 Bouguer (P.), height of freezing-point, 18 Boyle (R.), 16

C

Cailletet (L.), 112, 113 Cambridge, Mass., clouds measured at, 53 Castelli (B.), invented rain-gauge, 13 Cavallo (T.), showed lightness of hydrogen, 69 Celsius (A.), thermometer, 14 Charles (J. A. C.), ascent in hydrogen balloon, 19, 68 Cimento, Accademia del, 14 _Cirrus_ balloon, 106 Clayton (H. H.), 45, 47, 53, 62, 133, 147, 167 Cloud, amount of, 47 _et seq._ ---- atlases, 42, 43, 44 ---- Committee, International, 44, 65 ---- -year, international, 65 Clouds, classification of, 41 _et seq._ ---- definitions of, 45 ---- formation of, 39 ---- observations of direction and relative velocity, 51, 65 ---- measurements of height and velocity, 52, 53 _et seq._, 65, 121 ---- on Jupiter, 51 ---- relation to forecasting, 63-4 Cotte (L.), on clouds, 38 Coxwell (H.), aeronaut for Glaisher, 75 _et seq._ CrocÈ-Spinelli (J.), ascent in _Zenith_, 82 Cyclones, 59, 170

D

Dalton (J.), water-vapour in the air, 38 Daniell (J. F.), mountains a registering thermometer, 13 Davis (W. M.), cloud measurements, 53 Deluc (J. A.), theory of clouds, 42 De Saussure (H. B.), 20, 42, 73 ---- (H. B.), ascent of Mont Blanc, 20 Deutsche-Seewarte, Hamburg, 43 Donaldson (W. H.), proposed crossing Atlantic in a balloon, 92

E

Eddy (W. A.), 123, 124 _et seq._ Eiffel Tower, Paris, 23, 152 Ekholm (N.), 53, 92 Electricity, atmospheric, 70, 76, 121, 141 Espy (J. P.), kites to verify calculated height of clouds, 121 Etna, ascended by ancients, 12 Euler (L.), theory of kites, 118 Exploring the atmosphere, methods of, 35 _et seq._, 145-6

F

Fahrenheit (D. G.), thermometer, 14 Ferdinand II. (Grand Duke), distributed meteorological instruments, 17 Fergusson (S. P.), 35, 53, 126, 128, 131, 136 Ferrel (W.), theory of cyclones, 173 Flammarion (C.), balloon ascents, 81 Flying machines, future, 59, 174 Fonvielle (W. de), 81, 108 Fˆrster (W.), hypothesis of _Himmelsluft_, 28 Forecasting by kites, 143, 147 Franklin (B.), experiment with kites, 121, 123 Franklin Kite Club, 121

G

Galileo (G.), 14, 15 Gay-Lussac (J. L.), balloon ascent, 20, 73 German Emperor (William II.), patron of aeronautics, 86 ---- Society for Promotion of AÎrial Navigation, 86, 93, 106 Glaisher (J.), balloon ascents, 75 _et seq._, 93 Green (C.), aeronaut for Welsh, 74 Grimaldi (F. M.), first measured clouds trigonometrically, 52 Guericke (O. von), experiment of Magdeburg hemispheres, 16

H

Hagstrˆm (K.), measured clouds, 53 Halley (E.), measured heights by barometer, 17 Hann (J.), 36, 173 Han Sin, employed kites in warfare, 117 Hargrave (L.), invented cellular kite, 129 Harrington (M. W.), advocated exploring air with kites, 125 Harvard College Observatory, 35, 48 Hazen (H. A.), highest balloon ascent in America, 85 Height of balloon, Cailletet's apparatus for obtaining, 113 Heights of kite-flights at Blue Hill, 21, 140 ---- how measured by barometer, 17, 101 Heim (A.), voyage across the Alps, 92 Hellmann (G.), historical researches, 12 Helmholtz (H. von), wave-cloud, 40 Hergesell (H.), President of Aeronautical Committee, 108 Hermite (G.), 98, 99, 101 Hildebrandsson (H. H.), 42, 65 Hodgkins' Fund of Smithsonian Institution, grant from, 131 Howard (L.), cloud nomenclature, 41 Humboldt (A. von), 18, 20, 35 Humidity, changes with altitudes, 34, 71, 73, 77, 151, 169, 171 ---- diurnal changes at different altitudes, 153 ---- types of change with altitudes, 159 _et seq._ Hutton (J.), cause of precipitation, 38 Hygrometer, invention of, 13

J

Jeffries (J.), first scientific balloon ascent, 69 ---- first to cross the English Channel, 71 Jourdanet (D.), hypothesis of descent of man, 24 Jovis, balloon ascent, 84 Jupiter, analogy between cloudiness on earth and on, 51

K

Kepler (J.), height of atmosphere, 12 Kew Observatory, 53, 74, 122 Kˆppen (W.), cloud atlas, 43 Kirwan (R.), temperature at different latitudes, 18 Kite, antiquity of the, 117 ---- Eddy or Malay, 124, 129 ---- flights at Blue Hill, 21, 137, 140, 142 ---- Hargrave, 129, 132 ---- Lamson's "aero-curve," 134 ---- photography, 123, 126, 173 ---- theory of, 118, 124, 130 Kites, first scientific use of, 120 ---- first self-recording instruments raised by, 126 ---- oriental tailless, 118 ---- scientific uses of, 173 Kite-winch at Blue Hill, steam, 131, 136 Krakatoa, eruption of volcano, 27

L

Lamarck (J. B.), first to classify cloud forms, 41 Lamson (C. H.), aero-curve kite, 134 Langley (S. P.), 28, 174 Laplace (P. S. de), 17, 23, 101 Lavoisier (A. L.), 19, 68 Ley (W. C.), classification of clouds, 42 Lunardi (V.), balloon ascent, 69

M

M'Adie (A.), 53, 123 Magnetism, variation with height, 73, 77 Mallet (M.), balloon ascent, 84 Manila, Philippine Islands, cloud measurements at, 65-6 Mariotte (E.), law of gases, 16 Melvill (T.), aided in first scientific use of kites, 120 Merle (W.), oldest weather chronicles, 12 Meteorograph for kites, 128, 136 Meteorological conferences, international, 42, 44, 108 Meteorology, first treated by Aristotle, 10 ---- origin of, 10 Misti, El, highest station, 35 Montgolfier brothers, invented hot-air balloon, 19 M¸ntz (A.), analysis of air, 112-13

N

Nares (Sir G.), storm-kite, 122 Nebular hypothesis of Laplace, 23 Neumayer (G.), cloud-atlas, 42 Newton (I.), improved kites, 118

O

Olympus, mountain ascended by ancients, 11 Oxford, oldest weather chronicles, 12

P

Parseval (A. von), kite-balloon, 94 Pascal (B.), experiment with barometer, 15, 16 Perier (F.), _idem_, 15 Photography from balloons, 81, 113 ---- from kites, 123, 126, 173 Pickering (E. C.), pole-star recorder, 48 Pike's Peak, meteorological station, 35 Pil‚tre de Rozier (J. F.), first to ascend in balloon, 19 Pliny, the atmosphere, 9 Pocock (G.), great kite, 122 PoÎy (A.), classification of clouds, 42 Priestley (J.), oxygen in the air, 18

R

Rain-gauge, invention of, 13 RÈaumur (R. A. F. de), thermometer, 14 Rey (J.), first thermometer filled with liquid, 14 Riccioli (G. B.), first to measure clouds trigonometrically, 52 Richard (AbbÈ), clouds, 38 ---- (J.), self-recording instruments, 101, 125, 128, 136 Robertson (E. G.), 72, 73 ---- balloon ascent, 72 Rotch (A. L.), balloon ascents, 85, 86

S

Sacharoff, balloon ascent, 72 Siegsfeld (H. B. von), kite-balloon, 94 Sigsbee (C. D.), 44, 131 Sivel (T.), ascent in _Zenith_, 82 Spelterini (E.), balloon voyage with Heim, 92 Spencer (S.), aeronaut for Berson, 89 Sweetland (A. E.), prognostics from clouds, 63 Symons (G. J.), meteorologist and bibliophile, 12

T

Teisserenc de Bort (L.), 51, 116, 144 Temperature, change with height, 18, 29, 71, 73, 75, 77, 89, 90, 104, 107, 120, 121, 126, 141, 151, 167 ---- diurnal changes at different altitudes, 152, 161-2 ---- types of change with altitude, 154 _et seq._ Theodolite, registering, 106 Theophrastus, weather prognostics, 11 Thermometer, aspiration, 74, 86 ---- metallic, 116 ---- sling, 85 Thermometers, early, 14 Tissandier (A.), sketches of optical phenomena, 81 ---- (G.), ascent in _Zenith_, 81, 82 Toronto, Canada, international cloud measurements, 65 Torricelli (E.), invented barometer, 15 Tycho Brahe, height of atmosphere, 12

U

United States hydrographic office, 44 ---- weather bureau, 44, 65, 143 Upsala, Sweden, clouds measured at, 53, 58, 66

V

Violle (J.), 112, 115

W

Washington (Mount), meteorological station, 35 Weather chronicles, first, 12 ---- forecasting by means of clouds, 63 ---- prognostics of Aristotle and Theophrastus, 11 ---- vane, oldest meteorological instrument, 13 Weber (L.), measured electric potential with kites, 124 Welsh (J.), balloon ascents, 74 Wenz (E.), photography from kites, 123 Wilson (A.), first scientific use of kites, 120 Wind at different heights, 57 _et seq._, 98, 153, 170, 171 Wire for kite-lines, 123, 131, 134 Wise (J.), 84, 92 Woglom (J. T.), photography from kites, 123

Y

Young (C. A.), limit of atmosphere, 28

Z

_Zenith_, catastrophe of balloon, 82 Zero, absolute, 33

_Richard Clay & Sons, Limited, London & Bungay._

Transcriber's Notes

The text presented here is essentially that in the original printed volume. The list of corrections (CORRIGENDA) which accompanied the original has been applied. One additional typo (see below) has also been made. There may have been some minor corrections (missing period, commas, etc. added) which are not detailed here. In the original publication, several figures and plates were placed in the middle of paragrahs. Here most were moved between paragraphs. The List of Illustrations and any other page references still indicate the page number of the original location. On page 88, the "oe" ligature was replaced with the individual letters.

Typographical Correction

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