Part 1

Transcriber’s note: Table of Contents added by Transcriber. Boldface is indicated by =equals signs=; italics by _underscores_.

CONTENTS

The Coming Total Eclipse of the Sun 1 The Most Expensive City in the World 16 A Bubble-blowing Insect 23 The Negro Since the Civil War 29 The Birds of the Adirondacks 40 The Structure of Blind Fishes 48 A Hundred Years of Chemistry 59 Mount Tamalpais 69 International Law and the Peace Conference 76 The Fate of the Beagle 86 Science Study and National Character 90 Editor’s Table 99 Fragments of Science 101 Minor Paragraphs 108 Publications Received 111

THE POPULAR SCIENCE MONTHLY

EDITED BY J. McKEEN CATTELL

VOL. LVII MAY TO OCTOBER, 1900

NEW YORK AND LONDON McCLURE, PHILLIPS AND COMPANY 1900

COPYRIGHT, 1900, BY McCLURE, PHILLIPS AND COMPANY.

THE POPULAR SCIENCE MONTHLY

APPLETONS’ POPULAR SCIENCE MONTHLY.

MAY, 1900.

THE COMING TOTAL ECLIPSE OF THE SUN.

BY FRANK H. BIGELOW,

PROFESSOR OF METEOROLOGY, UNITED STATES WEATHER BUREAU.

The circumstance which renders the coming total eclipse of the sun, on May 28, 1900, of special significance to thousands of people who might otherwise entirely overlook the occasion is the fact that the path of the moon’s shadow over the surface of the earth, or the track of the eclipse, is in such a convenient locality--namely, in our Southern States--as to render the places of visibility easily accessible. Instead of being obliged to go to the ends of the earth, at a heavy expenditure of time and money, all the while running the risk of not seeing the eclipsed sun on account of prevailing cloudiness, we are fortunate this time to have the show at home in our own country. While many foreigners will be induced to come to the United States to make observations, it is certain that more people will be in a position to see this eclipse with a minimum amount of trouble than has ever happened before in the history of eclipses, at least since the telescope was invented and careful records of the phenomenon preserved.

The track of May 28th enters the United States in southeastern Louisiana; passes over New Orleans, La., centrally; over Mobile, Ala., which is on its southern edge; over Montgomery, Ala., on the northern edge; over Columbus, Ga.; south of Atlanta, Ga., which lies about twenty-five miles to the north of it; near Macon, Milledgeville, and Augusta, Ga., Columbia, S. C., Charlotte, N. C.; over Raleigh, N. C., which is ten miles north of the central line; and over Norfolk, Va., fifteen miles north of the center. The track is about fifty miles wide in all parts, and the duration of the eclipse varies from one minute and twelve seconds near New Orleans to one minute and forty-four seconds near Norfolk, on the central line. These durations diminish from the maximum at the middle of the track to zero at the northern and southern limits of it, so that an observer must be stationed as near the central line as possible in order to see much of the eclipse. The population of several of the above-mentioned cities is at present as follows: New Orleans, 242,000; Mobile, 31,000; Montgomery, 22,000; Columbus, 20,000; Atlanta, 66,000; Raleigh, 13,000; and Norfolk, 35,000. It is evident that with very little exertion more than 500,000 people can see this eclipse. It is most fortunate that the track passes near so many cities, because, with their facilities for the accommodation of visitors, many will be induced to undertake excursions with the purpose of taking in this rare sight, and a little enterprise on the part of railroads and transportation companies might easily increase the numbers. If people will go to a parade, yacht race, or an exposition, and consider themselves paid for their expenses, then surely they will find in this great spectacle of Nature not only an object of wonder and beauty, but also one of peculiar instruction in many important branches of science. All educators who can induce their pupils to make such an expedition will implant a love of astronomy in many impressionable minds which will become a source of pleasure to them for the rest of their lives.

Out of about seventy eclipses of the sun which have occurred somewhere in the world within the nineteenth century, there have been only eight total eclipses of more or less duration visible on the North American continent. The others happened in places often remote from civilization, and sometimes in entirely inaccessible localities, as over the ocean areas. The difficulty of transporting heavy baggage to the remote parts of Asia, Africa, or South America is such as to preclude all but a few scientists from any effort to observe eclipses. The writer was much impressed with the formidable nature of undertaking to establish eclipse stations in places which are distant from centers of population by his own experience on the West African Eclipse Expedition, sent out by the United States Government, for the eclipse of December 22, 1889, to Cape Ledo, on the west coast of Angola, about seventy miles south of St. Paul de Loanda. Nearly eight months were consumed in the course of the preparations at home and in the voyage out and back. The expedition, it should be said, however, went to Cape Town, South Africa, and halted also at St. Helena, Ascension Island, and Barbados for magnetic and gravity observations, so that all this time should not be charged to the eclipse proper. We sailed in the old frigate Pensacola, the companion to Farragut’s flagship, the Hartford, with Captain Yates. In earlier days Admiral Dewey commanded this ship, and the expedition was fitted out while he was in charge of the Bureau of Equipment at Washington. The same fine courtesy that has become so well known to his countrymen was at that time extended to all the members of the expedition.

The cloudiness along the track of the eclipse in the Southern States on the 28th of May, 1900, is evidently a matter of much importance not only for all astronomers, but for non-professional spectators. If it could be foretold, with the same precision as the astronomical data give the time and the place of the occurrence of the eclipse, that the day itself will be fair or cloudy, or that certain portions of the track will be clear while others will be obscured, it would be of great benefit. The cost of these scientific expeditions is very great, since it is necessary to transport many heavy and delicate pieces of apparatus into the field, including telescopes, spectroscopes, polariscopes, and photographic cameras, and set them up in exact position for the day of observation. The expedition to Cape Ledo, West Africa, in 1889, carried out a large amount of material, prepared it for work during the totality, and then entirely lost the sun during the critical moments by a temporary obscuring of the sky through local cloud formations. There had been some clouds at the station during the forenoons for several days preceding the eclipse, but the sky was usually clear and very favorable during the middle of the afternoons. The totality came on at three o’clock, and photographs of the sun were taken at first contact about 1.30 P. M.; clouds thickened, however, and totality was entirely lost, while the sun came out again for the last contact at 4.30 P. M. This was a very trying experience, and of course could not have been avoided by any possible precautions. Some astronomers have thought that the advance of the moon’s shadow is accompanied by a fall in temperature, and that cloudiness is more likely to be produced from this cause.

Soon after the West African eclipse Professor Todd, of Amherst College, proposed that more systematic observations be made for the probable state of the sky along eclipse tracks, with the view of at least selecting stations having the most favorable local conditions. The method was tried in Chili, April, 15, 1893, and in Japan, August 8, 1896, with some success. Heretofore the available meteorological records, which were originally taken for other general purposes, had been consulted, and some idea formed of the prevailing tendency to cloudy conditions. In accordance with the improved method, the United States Weather Bureau has been conducting special observations on the cloudiness occurring from May 15th to June 15th in each of the three years 1897, 1898, and 1899, for the morning hours of the eclipse--between 8 A. M. and 9 A. M. A tabular form was sent through the local offices to such observers as were willing to act as volunteers in making these records, and their reports have been studied to discover how the cloudiness behaves along the eclipse track at that season of the year. Each of the three years gives substantially the same conclusion--namely, that there is a maximum of cloudiness near the Atlantic coast in Virginia, extending back into North Carolina, and also near the Gulf coast in Louisiana and in southern Mississippi, while there is a minimum of cloudiness in eastern Alabama and central Georgia. The following table will serve to make this plain:

_The Prevailing Cloudiness of the Sky along the Eclipse Track._

+--------------+------------------ STATE. | General sky. | Sky near the sun. -------------------+--------------+------------------ Virginia | 40.3 | 38.0 North Carolina | 32.4 | 29.9 South Carolina | 26.4 | 24.9 Georgia | 16.4 | 14.7 Alabama | 18.2 | 17.7 Mississippi | 30.8 | 29.2 Louisiana | 32.9 | 27.7 -------------------+--------------+------------------

The significance of these figures is shown by transferring them to a diagram, given on Chart II, which indicates the average cloudiness prevailing over the several States where they are crossed by the track. The marked depression in the middle portions, especially over Alabama and Georgia, indicates that the stations in these districts make a much better showing than those nearer the coast line. The reasons for this difference are probably many in number, but the chief feature is that the interior of this region, especially over the higher lands of the southern reaches of the Appalachian Mountains, which are from six hundred to one thousand feet above the sea level, is somewhat freer from the moisture flowing inland from the ocean at that season of the year. The table shows also two divisions, one for the “general sky,” wherein the relative cloudiness was noted in every portion of the visible sky, and for the “sky near the sun,” where the observation was confined to the immediate vicinity of the sun. The two records agree almost exactly, except that the sky near the sun averages a little lower than the general sky. This indicates that although the sun will be seen in the morning hour of May 28th, when it is only from thirty to forty degrees above the horizon, yet this is not an unfavorable circumstance. The low altitude, on the other hand, makes it easier for those at the instruments to enjoy a more comfortable observing position than if it were nearer the zenith, where one must look directly upward. Of course, a storm of some kind may occur on that day to modify these general weather conditions and upset all calculations. While the cloud observations suggest that Georgia and Alabama have the best sites for the eclipse, it must be remembered that the duration is about one minute and twenty seconds in Alabama, and one minute and forty seconds in North Carolina. As a gain of twenty seconds in observing time will be considered by many of sufficient importance to take chances on the cloudiness, stations will be selected in North Carolina for that reason, although the probability for minimum cloudiness is twice as good in Georgia and Alabama. The table shows that the chances are only one to six against observers located in these States, while near the coast they are about two to six against them. On the whole, the general result is that observing in this region ought to be successful, because the favorable chances for good weather are above the average at that season of the year.

On Chart I there are six lines drawn across the track: No. 1 near New Orleans, and No. 6 on the ocean to the east of Norfolk, Va. These represent the places for which the times of the duration are computed in the American Nautical Almanac, with the following results:

No. h. m. h. m. m. s. 1. At 1 30 Greenwich M. T. = 7 27. Local M. T. the duration is 1 12.6 2. ” 1 35 ” ” = 7 47. ” ” ” ” ” 1 19.6 3. ” 1 40 ” ” = 8 05. ” ” ” ” ” 1 26.0 4. ” 1 45 ” ” = 8 22. ” ” ” ” ” 1 31.7 5. ” 1 50 ” ” = 8 40. ” ” ” ” ” 1 37.0 6. ” 1 55 ” ” = 8 54. ” ” ” ” ” 1 41.9

An observer at the intersection of these cross-lines with the central line will see the totality during the intervals given in the table.

The mode of the formation of the shadow cones of the moon, called the penumbra for the partial shadow and the umbra for the total shadow, are well illustrated in general works on astronomy, and good geometrical pictures of them can there be found, together with much useful information regarding the subject of eclipses. As we are here concerned chiefly with certain practical points about the eclipse of 1900, it will be well for the reader to consult such works for many details regarding the astronomical features attending an eclipse of the sun which must now be omitted.

There are many existing theories to account for the phenomenon of the sun’s bright appendage, called the corona, which is visible only during eclipses, on account of the absorbing effects of the earth’s atmosphere on its light. Is it electrical, or is it magnetic? Is it composed of fine stuff ejected from the sun, or of meteoric dust falling upon the sun? Is it merely an optical effect, as some suppose, or is it a portion of the newly discovered radiant matter streaming off to enormous distances into space? The answer to these questions is eagerly sought through observation, photography, and every other possible means, on the occasion of each total eclipse.

The efforts of astronomers have thus far secured a series of pictures of the solar corona, which, when compared together, show very distinctly that the corona, as well as the spots, the protuberances, and the faculæ, are going through a series of changes which seem to repeat themselves in the so-called eleven-year period. It has also been proven, with entire distinctness, that the earth’s magnetic field, as marked by the changes in the intensity of the magnetic elements, in the auroral displays, and the earth electric currents show variations which synchronize closely with those observed on the sun; also that the weather elements of pressure, temperature, precipitation, and storm intensity all harmonize with the solar and the earth’s magnetism in the same synchronism. All attempts of scientists to detect any variations in the sunshine which falls upon the tropics have been entirely futile; on the other hand, it has been shown that the magnetic forces having the characteristics just mentioned impinge upon the earth in a direction perpendicular to the plane of the earth’s orbit, just as if the sun, being a magnet, throws out a field of force to the surface of the earth, which, by its variation depending upon the internal workings of the sun, produces the changes just enumerated in the earth’s atmosphere and in its magnetic field, also throughout the planetary system, being, of course, strongest near the sun. The belief is gradually growing among scientists that the earth, the sun, and the planets are all magnetic bodies, and have these bonds of connection between them in addition to the Newtonian gravitation. This is a most fascinating field of research, and, though full of difficulties, yet attracts the attention of many who are convinced that one of the most pressing duties of the hour is to clear up the problems connected with the transmission of energy from the sun to the earth in other forms than the ordinary or sunlight radiation. It is entirely probable that the secular variations of the weather changes from year to year, and even from month to month, are bound up with these solar forces, and that the solution of these questions will carry with them much information of practical use to civilized man.

The coronas of the past forty years are shown on Chart III, taken from the report of the eclipse of 1896 (August 9th), by A. Hansky. It arranges the coronas in the eleven-year period so far as the dates at which the eclipses occurred permit this to be done, and by comparing them in vertical lines the similarity is at once seen for the respective quarters of phases of the period. The forecast there given for 1900 is seen to resemble 1867, 1878, and 1889, but it differs in orientation from that on Chart IV, which was prepared by the author. The four coronas on the left in Chart III are taken at the sun-spot maximum, and the appearance is that of total confusion in the structure of the rays; the second and the fourth columns are for the sun’s medium intensity at about halfway between the maximum and the minimum, and they show a system of polar rays taking on structural form, the second column being at a stage of diminishing and the fourth at one of increasing solar activity; the third column gives the corona when the spots are at a minimum of frequency and the sun is in a comparatively quiescent state, wherein the polar rifts are very distinct and the equatorial wings or extensions greatly developed.

The successful observation of a solar corona depends upon three conditions: the selection of the instrument, its proper mounting, and the photographic process, regarding each of which a few suggestions will be made. The instruments are divided into two classes, for visual and for photographic work. But in either case the most important feature is the focal length or the size of the telescope. Since the photographic image of the corona will not bear magnifying without dispersing the available light, and thus blurring out the details of the picture, which is the most important feature to retain to the utmost, one can not use a short telescope and at the same time a magnifying eyepiece to enlarge the image by projection on a screen or on a photographic plate. The only alternative in order to get an image of large diameter is to use a long-focus lens. The effect of a difference of focus upon the image of the corona is well shown on Chart V, which gives a small corona (1) taken with a four-foot lens (Barnard), (2) with a fifteen-foot lens (Pickering), and (3) with a forty-foot lens (Schaeberle). The diameter is proportional to the focal length, but the difference of effect upon the details is very important. In the small picture the details of the corona near the sun are completely lost in the general light, while the coronal extensions from the middle latitudes are seen at a great distance from the sun--as much as one million miles; at the same time the polar rifts are distinctly marked, so that the pole or central line from which they bend is readily located. On the second picture the details of the polar rays are better brought out, but the extensions are shortened. In the third the region near the sun’s edge has many interesting details very clearly defined, while all the extensions are gone. It is evident that each lens has its advantage, according to the details sought, and they ought all to be employed in the eclipse. The reproductions on paper by no means do justice to the original negatives, which make the distinctions even more pronounced than shown on Chart V.