Chapter 9

The mobility of air seems almost preternatural, when the proper conditions for setting a current in motion are supplied. But without a current established, it is surprising in turn to find how obstinately and elusively immovable it can be. It is like tossing a feather; or trying to drive a swarm of flies; dodging and evading every impulse applied. But, given a flue, to define and conduct a stream; an upright flue, to take advantage of the slighter gravity of the warmed air within it; and a flue contracted at the inlet and expanded as it rises, so as to free, diffuse, and lighten the column of air, toward the exit; _then_, initiate an induced current of air at the inlet, by the injection of a jet of gas in the state of semi-explosive action called flame; the pressure pushing upward from the crowded entrance finds easier way and less resistance the farther it goes in the expanding flue; the warmth and reduced gravity of the stream comes in as an auxiliary in overcoming friction and any exceptional obstruction in the state of the atmosphere; and now, as the ball is once set rolling, with a little _aid_ instead of resistance from gravitation, its initial impulse all the while sustained by the gas jet, and friction reduced to a very small incident--there is nothing to prevent the current rolling on with accelerated velocity (within the limitations imposed by increasing friction) and rolling on forever. I might, if I had time, add a curious consideration of the law of _vortex motion_ in elastic fluids, demonstrated by Helmholtz, which relieves the motion of such fluids from friction, as wheels facilitate the movement of a solid; and which also sucks into the rolling vortex the contiguous air, thus entraining it, as we have seen, so much more effectively than could be done by a direct and rigid current, like a jet of water, for instance. A wheel set in motion on an almost frictionless bearing of metalline, runs without perceptible abatement of velocity, until one begins to involuntarily question whether it will ever stop. In the all but free winds that roll with minimized friction in the higher atmosphere, there seems to be a self-moving force; so persistent is simple momentum in a mass so infinitesimally obstructed and so infinitely wheeled. An active current of air in a ventilating flue is only less perfect in the same conditions; and so it is quite conceivable, and not incredible, that such a current may be gradually established and thenceforward permanently maintained by a small motor flame barely more than enough to overbalance the minimized friction. This is not a supposed or theoretically inferred fact, like the facts of ventilation sometimes alleged by theorists. On the contrary, the theory I have offered is merely an attempt to explain facts that I have witnessed and that anyone can verify with the anemometer. But the _theory_ by no means covers the art and mystery of ventilation; for ventilation is truly an _art_ as well as a mystery. The art lies in a consummate experience of the sizes, proportions, and forms of flues, their inlets, expansions, and exits, with many other incidental adaptations necessary, in order to insure under _all_ circumstances the regular exhaustion of any specific volume of air required, per minute. And this art has by one man been achieved. It would be a double injustice if I should neglect from any motive to inform my audience to whom I am indebted for what I know about ventilation practically, and even for the knowledge that there is any such fact as a practicable ventilation of houses; one who is no theorist, but who has felt his way experimentally with his own hands, for a lifetime, to a practical mastery of the art to which I have attempted to fit a theory; every one present who is well informed on this subject must have anticipated already in mind the name of Henry A. Gouge.

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THE RECENT ERUPTION OF ETNA.

On the morning of the 20th of March, a long series of earthquakes spread alarm throughout all the cities and numerous villages that are scattered over the sides of Mt. Etna. The shocks followed each other at intervals of a few minutes; dull subterranean rumblings were heard; and a catastrophe was seen to be impending. Toward evening the ground cracked at the lower part of the south side of the mountain, at the limit of the cultivated zone, and at four kilometers to the north of the village of Nicolosi. There formed on the earth a large number of very wide fissures, through which escaped great volumes of steam and gases which enveloped the mountain in a thick haze; and toward night, a very bright red light, which, seen from Catania, seemed to come out in great waves from the foot of the mountain, announced the coming of the lava.

Eleven eruptions occurred during the night, and shot into the air fiery scoriæ which, in a short time, formed three hillocks from forty to fifty meters in height. The jet of scoriæ was accompanied with strong detonations, and the oscillations of the ground were of such violence that the bells in the villages of Nicolosi and Pedara rang of themselves. The general consternation was the greater in that the locality in which the eruptive phenomena were manifesting themselves was nearly the same as that which formed the theater of the celebrated eruption of 1669. This locality overlooks an inclined plane which is given up to cultivation, and in which are scattered, at a short distance from the place of the eruption, twelve villages having a total population of 20,000 inhabitants. On the second day the character, of the eruption had become of a very alarming character. New fissures showed themselves up to the vicinity of Nicolosi, and the lava flowed in great waves over the circumjacent lands. This seemed to indicate a lengthy eruption; but, to the surprise of those interested in volcanic phenomena, on the third day the eruptive movement began to decrease, and, during the night, stopped entirely. This was a very fortunate circumstance, for this eruption would have caused immense damages. It cannot be disguised, however, that the eruptive attendants of this conflagration remain under conditions such as to constitute a permanent danger for the neighboring villages. It has happened, in fact, that in consequence of the quick cessation of the eruption, those secondary phenomena through which nature usually provides a solid closing of the parasitic craters have not occurred. So it is probable that when a new eruption takes place it will be at the same point at which manifested itself the one that has just abated.--_La Nature_.

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PHYSICS WITHOUT APPARATUS.

Take an ordinary wine bottle and place it in front of and within a few inches of a lighted candle. Blow against the bottle with your mouth at about four or six inches distant from it and in a line with the flame. Very curiously, notwithstanding the presence of the bottle and its interception of the current of air, the candle will be immediately extinguished as if there were no obstacle in the way. This phenomenon is readily understood when we reflect that the bottle receives the current of air on its polished surface and divides it into two, one of which is guided to the right and the other to the left. These two currents, after separating and driving back the surrounding air, meet again at the very spot at which the flame is situated, and extinguish the candle.

It is evident that the experiment can be reproduced by putting the candle behind a stove pipe, a cylinder of glass or metal, a cylindrical tin box, or any other object of the same form with a diameter greater than that of a bottle, but not having a rough or angular surface, since the latter would cause the current to be lost in the surrounding air.

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THE TRAVELS OF THE SUN.

Some recent discussions of the constitution of the sun have turned in part upon what is known as the sun's proper motion in space. This is one of the most surprising and interesting things that science has ever brought to light, and yet it is something of which comparatively few persons have any knowledge. It is customary to look upon the sun as if it were the center of the universe, an immovable fiery globe around which the earth and other planets revolve while it remains fixed in one place. Nothing could be further from the truth. The sun is, in fact, the most wonderful of travelers. He is flying through space at the rate of not less than a hundred and sixty millions of miles in a year, and the earth and her sister planets are his fellow voyagers, which, obeying his overpowering attraction, circle about him as he advances. In other words, if we could take up a position in open space in advance of the sun, we should see him rushing toward us at the rate of some 450,000 miles a day, chased by his whole family of shining worlds and the vast swarms of meteoric bodies which obey his attraction.

The general direction of this motion of the solar system has been known since the time of Sir William Herschel. It is toward the constellation Hercules, which, at this season, may be seen in the northeastern sky at 9 o'clock in the evening. As the line of this motion makes an angle of fifty odd degrees with the plane of the earth's orbit, it follows that the earth is not like a horse at a windlass, circling around the sun forever in one beaten path, but like a ship belonging to a fleet whose leader is continually pushing its prow into unexplored waters.

The path of the earth through space is spiral, so that it is all the time advancing into new regions along with the sun. She is on a boundless voyage of discovery, and her human crew are born and die in widely separated tracts of space. Think of the distance over which the travels of the sun have borne the earth only since the beginning of human history! Six thousand years ago the earth and sun were about a million millions of miles further from the stars in Hercules than they are to-day. Columbus and his contemporaries lived when the earth was in a region of the universe more than sixty thousand millions of miles from the place where it is now, so that since his time the whole human race has been making a voyage through space, in comparison with which his longest voyage was as the footstep of a fly.

Thus the great events in the history of the world may be said to have occurred in different parts of the universe. An almost inconceivable distance separates the spot which the earth occupied in the time of Alexander from that which it occupied when Cæsar invaded Gaul. The sun and the earth have wandered so far from their birthplace that the mind staggers in the attempt to guess at the stupendous distance which now probably separates them from it. It may be that the motion of the solar system is orbital and that our sun and many of the stars, his fellow suns, are revolving around some common center, but if so, no means has yet been devised of detecting the form or dimensions of his orbit. So far as we can see, the sun is moving in a straight line.

Since space is believed to be filled with some sort of ethereal medium, curious consequences are seen to follow from the motions that have been described. A solid globe like the earth rushing at great speed through such a medium will encounter some resistance. If the medium be exceedingly rare, as it must be in fact, the resistance will be correspondingly small, but still there will be resistance. If the sun stood still, the earth, owing to the inclination of its axis to the plane of its orbit, around the sun, would encounter the resistance of the ether principally on its northern hemisphere from summer to winter, and on its southern hemisphere from winter to summer. But in consequence of the motion of the sun shared by the earth, this law of distribution is changed, and from summer to winter the earth plows through the ether with its north pole foremost, while from winter to summer, although the resistance of the ether is encountered more evenly by the two hemispheres, yet it is still felt principally in the northern hemisphere, and the south pole remains practically protected. It follows that the southern hemisphere, and particularly the south polar regions are more or less completely sheltered the whole year around. It might then be supposed that the impact of the particles of the ether shouldered aside by the earth in its swift flight and the compression produced in front of the advancing globe would tend to raise the temperature of the northern hemisphere as compared with the southern hemisphere, while the south pole, being more or less directly in the wake of the earth, and in a region of rarefaction of the ether, would constantly possess a remarkably low temperature.

Now, it is known that the south polar regions are more covered with ice and snow than those of the north, and that the temperature there the year around is lower. Whether this difference is owing to the effects of the earth's journey through the ether, is a question.

The sun, too, moves with his northern hemisphere foremost, and it is worthy of remark that it has been suspected that the northern hemisphere of the sun radiates more heat than the southern.

But whatever effect it may or may not have upon the meteorological condition of the earth, the fact that the solar system is thus voyaging through space is in itself exceedingly interesting. Not the wildest traveler's dream presents to the imagination such a voyage as this on which every inhabitant of the earth is bound. A glance at a star map shows that the direction in which we are going is carrying us toward a region of the heavens exceedingly rich in stars, many, and perhaps most, of which are greater suns than ours. There can be little doubt that when the sun arrives in the neighborhood of those stars, he will be surrounded by celestial scenery very different from and much more brilliant than that of the region of space in which he now is. The inhabitants of the globe at that distant period will certainly behold new and far more glorious heavens, though the earth may be unchanged.--_N.Y. Sun._

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PROPAGATION OF MAPLE TREES.

I do not presume that all people over three score years of age are so entirely ignorant as I am, but probably there are some. I have lived more than sixty years almost in the woods, and I never observed, and never heard any other person speak of, the blooming, seeding, and maturing of the water maple. I have a beautiful low of water maple shade trees along the street in front of my house. In March, 1882, I observed that they were in bloom, and many bees were swarming about them. After the bees left them I noticed the seed (specimens inclosed of this spring's growth) in millions. As the leaves put out in April the little knife blade seeds fell off, so thick as to almost cover the ground. My grandson picked up three or four hatfuls, and I sent the seed to my farm and had them drilled in like wheat, when I planted corn. The result is I have from 300 to 500 beautiful maples from 6 inches to three feet high. I noticed the blooms again this spring, but a cold snap killed the blooms, and only now and then can I find a seed. I had a sugar tree in my yard, which bloomed and bore seed which did not fall off through the summer. My yard now has as many little sugar trees as it has leaves of blue grass.

It strikes me that the gathering and planting of maple seed is the best way to wood the prairies of the West and the worn-out lands of the Eastern and Middle States. The tree is valuable for shade and for timber, and is as rapid in growth as any tree within my knowledge. I noticed some trees of this sort yesterday which are from 2½ to 3½ feet in diameter. The lumber from such timber makes beautiful furniture. This is intended only for those who have been as non-observant as myself, and not the wise, who are always posted.

Franklin, Tenn. J.B.M.

The seeds inclosed were the samaras of _Acer rubrum_, called the "soft" maple in many localities, and "red" maple in others. We have seen trees only three or four inches in diameter full of blossoms. This is one of the earliest trees to bloom in spring, and the pretty winged samaras soon mature and fall. The sugar maple, _Acer saccharinum_, blossoms later, and the seeds are persistent till autumn, and lie on the ground all winter before germinating. The lumber from this latter is more valuable than soft maple, being harder, heavier, and taking a better polish. Soft maple makes an ox-yoke which is durable and not heavy. In early times a decoction of the bark was frequently used for making a black ink.--_Country Gentleman._

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DIOSCOREA RETUSA.

One of the most elegant plants one can have in a greenhouse is this twiner, a native of South Africa. It has slender stems clothed with distinctly veined leaves, and produces a profusion of creamy white fragrant flowers in pendulous clusters, as shown in the annexed engraving, for which we are indebted to Messrs Veitch of Chelsea, who distributed the plant a few years ago. On several occasions Messrs Veitch have exhibited it trained parasol fashion and covered abundantly with elegant drooping clusters of flowers, and as such it has been much admired. When planted out in a warmish greenhouse and allowed to twine at will around an upright pillar, it is seen to the best advantage, and, though not showy, makes a pleasing contrast with other gayly tinted flowers. It is so unlike any other ornamental plant in cultivation, that it ought to become more widely known than it appears to be at present.--_The Garden._

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RAVAGES OF A RARE SCOLYTID BEETLE IN THE SUGAR MAPLES OF NORTHEASTERN NEW YORK.

About the first of last August (1882) I noticed that a large percentage of the undergrowth of the sugar maple (_Acer saccharinum_) in Lewis County, Northeastern New York, seemed to be dying The leaves drooped and withered, and finally shriveled and dried, but still clung to the branches.

The majority of the plants affected were bushes a centimeter or two in thickness, and averaging from one to two meters in height, though a few exceeded these dimensions. On attempting to pull them up they uniformly, and almost without exception, broke off at the level of the ground, leaving the root undisturbed. A glance at the broken end sufficed to reveal the mystery, for it was perforated, both vertically and horizontally, by the tubular excavations of a little Scolytid beetle which, in most instances, was found still engaged in his work of destruction.

At this time the wood immediately above the part actually invaded by the insect was still sound, but a couple of months later it was generally found to be rotten. During September and October I dug up and examined a large number of apparently healthy young maples of about the size of those already mentioned, and was somewhat surprised to discover that fully ten per cent. of them were infested with the same beetles, though the excavations had not as yet been sufficiently extensive to affect the outward appearance of the bush. They must all die during the coming winter, and next spring will show that, in Lewis County alone, hundreds of thousands of young sugar maples perished from the ravages of this Scolytid during the summer of 1882.

Dr. George H Horn, of Philadelphia, to whom I sent specimens for identification, writes me that the beetle is _Corthylus punctatissimus_, Zim, and that nothing is known of its habits. I take pleasure, therefore, in contributing the present account, meager as it is, of its operations, and have illustrated it with a few rough sketches that are all of the natural size, excepting those of the insects themselves, which are magnified about nine diameters.

The hole which constitutes the entrance to the excavation is, without exception, at or very near the surface of the ground, and is invariably beneath the layer of dead and decaying leaves that everywhere covers the soil in our Northern deciduous forests. Each burrow consists of a primary, more or less horizontal, circular canal, that passes completely around the bush, but does not perforate into the entrance hole, for it generally takes a slightly spiral course, so that when back to the starting point it falls either a little above, or a little below it--commonly the latter (see Figs. 1 and 2).

It follows the periphery so closely that the outer layer of growing wood, separating it from the bark, does not average 0.25 mm. in thickness, and yet I have never known it to cut entirely through this, so as to lie in contact with the bark.

From this primary circular excavation issue, at right angles, and generally in both directions (up and down), a varying number of straight tubes, parallel to the axis of the plant (see Figs. 1, 2, and 3). They average five or six millimeters in length, and commonly terminate blindly, a mature beetle being usually found in the end of each. Sometimes, but rarely, one or more of those vertical excavations is found to extend farther, and, bending at a right angle, to take a turn around the circumference of the bush, thus constituting a second horizontal circular canal from which, as from the primary one, a varying number of short vertical tubes branch off. And in very exceptional cases these excavations extend still deeper, and there may be three, or even four, more or less complete circular canals. Such an unusual state of things exists in the specimen from which Fig 3 is taken.

It will be seen that with few exceptions, the most important of which is shown in Fig 4, all the excavations (including both the horizontal canals and their vertical off shoots) are made in the sap-wood immediately under the bark, and not in the hard and comparatively dry central portion. This is, doubtless, because the outer layers of the wood are softer and more juicy, and therefore more easily cut, besides containing more nutriment and being, doubt less, better relished than the drier interior.

This beetle does not bore, like some insects, but devours bodily all the wood that is removed in making its burrows. The depth of each vertical tube may be taken as an index to the length of time the animal has been at work, and the number of these tubes generally tells how many inhabit each bush, for as a general rule each individual makes but one hole, and is commonly found at the bottom of it. All of the excavations are black inside.

The beetle is sub-cylindric in outline, and very small, measuring but 3.5 mm in length. Its color is a dark chestnut brown, some specimens being almost black. Its head is bent down under the thorax, and cannot be seen from above (see Fig. 5).

Should this species become abundant and widely dispersed, it could but exercise a disastrous influence upon the maple forests of the future--_G. Hart Merriam, M D, in American Naturalist._

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THE RED SPIDER.

(_Tetranyehus telarius._)