Chap. 1.] Lizards, Frogs, &c. against Gravity. 183 the insect possess over them! It would seem as if they turned their bodies in various directions, by diminishing the velocity of one wing, and increasing that of the other; and also by varying the angle at which they strike the air, and descend by closing them or stopping their vibrations. And with what vigor and celerity must one of these insects move its delicate wings in order to elevate its comparatively heavy body! Yet this movement is made quick as the others. It bounds upwards, like a balloon released from its cords; now sailing through a room, sweeping round our heads, buzzing at our ears, skimming over the floor, and anon inverting its body and resting on the ceiling! And all this within two or three seconds of time, and without any apparent exertion or fatigue. Here is a fruitful subject of inquiry to the machinist and aëronaut. All the wonders that the automatons of Maelzel and Maillardet ever wrought, are nothing compared to those that may yet be accomplished by studying the organization and motions of these living machines. But there are larger animals than flies that suspend themselves in an inverted position. Mr. Marsden, in his "History of Sumatra," (London, 1811, p. 119) mentions lizards four inches long, which, he observes, are the largest reptiles that can walk in an inverted situation. One of them, of size sufficient to devour a cockroach, runs on the ceiling of a room, and in that situation' seizes its prey with the utmost facility. Sometimes, however, when springing too eagerly at a fly, they lose their hold, and drop to the floor. The Gecko of Java and other countries is furnished with similar apparatus in its feet, by means of which it runs up the smoothest polished walls, and even carries a load with it, equal in weight to that of its own body. Osbeck mentions lizards in China that ran up and down the walls with such agility as they can scarce be caught." The tree frog of this country adheres to the leaves of trees by the tubercles on its toes: a young one has sustained itself in an inverted position against the under side of a plate of glass. From the observations of E. Jesse, author of 'Gleanings of Natural History' it appears that common frogs can occasionally do the same. His account is very interesting: "I may here mention a curious observation I made in regard to some frogs that had fallen down a small area which gave light to one of the windows of my house. The top of the area being on a level with the ground, was covered over with some iron bars through which the frogs fell. During dry and warm weather when they could not absorb much moisture, I observed them to appear almost torpid; but when it rained they became impatient of their confinement, and endeavored to make their escape, which they did in the following manner. The wall of the area was about five feet in height and plastered and white-washed as smooth as the ceiling of a room; upon this surface the frogs soon found that their claws would render them little or no assistance; they therefore contracted their large feet so as to make a hollow in the centre, and by means of the moisture which they had imbibed in consequence of the rain, they contrived to produce a vacuum, so that by the pressure of the air on their extended feet, (in the same way that we see boys take up a stone by means of a piece of wet leather fastened to a string) they ascended the wall and made their escape. This happened constantly in the course of three years."-Phil. Ed. 1833. p. 140. Innumerable crustaceous animals adhere to rocks and stones by the same principle. But it is not the smaller inhabitants of either the land or the sea, as flies, spiders, butterflies, bees, &c. some of which scarcely weigh a grain; or lizards and frogs, &c. of five or six ounces, which thus sustain themselves against gravity; for the enormous walrus, that sometimes ex 184 Sucking Fish. [Book II ceeds a ton in weight, is furnished by the Creator with analogous apparatus in his hinder feet; and thus climbs by atmospheric pressure, the glassy surfaces of ice-bergs. How forcibly do these examples illustrate the intimate connection which subsists between the various departments of Natural Philosophy. A knowledge of one always furnishes a key (whether it be used or not) to open some of the mysteries of another. Thus a person who understands the principle by which water is raised in a simple pump, can by it explain some of the most surprising facts in the natural history of animals; and solve problems respecting the motions and organs of motions of numerous tribes of animated beings, which two or three centuries ago, the most enlightened philosophers could not comprehend. And with a simple pump, he can moreover determine, as with a barometer, the measurement of all accessible heights, and with a degree of accuracy that, in some cases, is deemed preferable to geometrical demonstrations. When two substances are brought together, at some distance below the surface of water, and so as to exclude it from between them, they are then pressed together with a force greater than when in the air, because the weight of the perpendicular column of water over them is then added to that of the atmosphere. Numerous examples of this combined pressure are also to be found in the natural world. By it, various species of fish adhere to rocks and stones in the depths of the sea, from which they cannot be separated except by tearing their bodies asunder. Some by means of it attach themselves to the bodies of others, and thereby traverse the ocean without any expense or exertion of their own, somewhat like dishonest travelers, who elude the payment of their fare. There are several species of fishes known which have a separate organ of adhesion, and there are doubtless many more which have not yet come under the observation of man. The most celebrated is the remora or sucking fish of Dampier and other navigators. It is, in size and shape, similar to a large whiting, except that the head is much flatter. "From the head to the middle of its back, (observes Dampier) there groweth a sort of flesh of a hard gristly substance, like that of the limpet. This excrescence is of a flat oval form, about 7 or 8 inches long, and 5 or 6 broad, and rising about half an inch high. It is full of small ridges with which it will fasten itself to any thing that it meets with in the sea. When it is fair weather and but little wind, they will play about a ship, but in blustering weather, or when the ship sails quick, they commonly fasten themselves to the ship's bottom, from whence neither the ship's motion, though never so swift, nor the most tempestuous sea can remove them. They will likewise fasten themselves to any bigger fish, for they never swim fast themselves, if they meet with any thing to carry them. I have found them sticking to a shark after it was hal'd in on deck, though a shark is so strong and boisterous a fish, and throws about him so vehemently when caught, and for half an hour together, that did not the sucking fish stick at no ordinary rate, it must needs be cast off by so much violence." They are familiar to most of our seamen. Other species have a circular organ of adhesion, consisting of numerous soft papillæ, and placed on the thorax, instead of the top of the head, as in the remora. In some fish the ventral fins are united and are capable of adhesion. In the lamprey the mouth contracts and a Dampier's Voyages, vi. edit. 1717. Vol. i, 64, and Vol. ii, part iii, p. 110. In the the plates of Vol. iii, is a figure of one. Figures of the excrescence or sucking part of the remora, and of the feet of the house-fly, may be seen in Dr. Brewster's Letters on Natural Magic. Chap. 1.] The Remora. 185 acts as a sucker; while that curious animal the cuttle fish secures the victims that fall into its fatal embraces by the suckers on its arms. The prodigious pressure that, at great depths, unites these inhabitants of the sea to their prey, led man to employ them to hunt the sea for his benefit as well as their own. Both the remora and lamprey tribe have been used for this purpose. Columbus when on the coast of St. Domingo was greatly surprised on beholding the Indians of that island fishing with them. "They had a small fish, the flat head of which was furnished with numerous suckers, by which it attached itself so firmly to any object as to be torn_in pieces rather than abandon its hold. Tying a long string to the tail, the Indians permitted it to swim at large: it generally kept near the surface till it perceived its prey, when darting down swiftly it attached itself to the throat of a fish, or to the under shell of a tortoise, when both were drawn up by the fisherman." Ferdinand Columbus saw a shark caught in this manner.a The same mode of fishing was followed at Zanguebar, on the eastern coast of Africa. The inhabitants of the coast when fishing for turtle, "take a living sucking fish or remora, and fastening a couple of strings to it, (one at the head and the other at the tail) they let the sucking fish down into the water on the turtle ground, among the half grown or young turtle; and when they find that the fish hath fastened himself to the back of a turtle, as he will soon do, they draw him and the turtle up together. This way of fishing as I have heard is also used at Madagascar." The remora was well known to the ancients. History has preserved a fabulous account of their having the power to stop a vessel under sail, by attaching themselves to her rudder. A Roman ship belonging to a fleet, it is said, was thus arrested, when she "stoode stil as if she had lien at anker, not stirring a whit out of her place." There is another illustration of the enormous pressure that fishes endure at great depths. The small volume of air that is contained in the bladder, and by the expansion and contraction of which they ascend and descend, is at the bottom of the sea compressed into a space many times smaller than when they swim near the surface. (At 33 feet from the surface it occupies but one half.) Hence, it frequently occurs that when such fish are suddenly drawn up, (as the cod on the banks of Newfoundland) the membrane bursts, in consequence of the diminished pressure, and the air rushing into the abdomen, forces the intestines out of the mouth. From a similar cause, blood is forced out of the ears of divers, when the bell that contains them is quickly drawn up. This pressure is also evinced in the fact that the timber of foundered vessels never rises, because the pores become completely filled with water by the pressure of the superincumbent mass, and the wood then becomes almost heavy as iron.' The pressure of the atmosphere on liquids is equally obvious. When a bucket or other vessel is sunk in water and then raised in an inverted position, the air being excluded from acting on the surface of the liquid. within, still presses on that without, so that the water is suspended in the vessel; and if the under surface of the liquid could be kept level and at rest, water might be transported in buckets thus turned upside down, as effectually as in the ordinary mode of conveying it The experiment with a goblet or tumbler presents a very neat illustration. One of these filled with water, and having a piece of writing paper laid over it, and held close till the vessel be inverted, will retain the liquid a Irving's Columbus, Vol. i, 273. Dampier's Voyages, Vol. ii, part ii, 108. 186 Atmospheric Pressure on Laquids. [Book II. within it. In this experiment the paper merely preserves the liquid surface level: it remains perfectly free and loose; and so far from being close to the edge of the glass, it may, while the latter is held in a horizontal position, be withdrawn several lines from it without the water escaping; and it may be pierced full of small holes with the same effect. If an inverted vessel be filled with any material that excludes the air, and whose specific gravity is greater than that of water, when lowered into the latter, the contents will descend and be replaced by the water. A bottle filled with sand, shot, &c. and inverted in water, will have its contents exchanged for the latter. As these substances, however, do not perfectly fill the vessel, and of course do not exclude all the air, the experiment succeeds better when the vessel contains heavy liquids, as mercury, sulphuric acid, &c. It is said that negroes in the West Indies often insert the long neck of a bottle filled with water, into the bung-holes of rum puncheons, when the superior gravity of the water (in this case) descends, and is gradually replaced with the lighter spirit. In the preceding examples and those in subsequent chapters, it will be found that wherever a vacuity or partial vacuum is formed, the adjacent air, by the pressure above, rushes in and drives before it the object that intervenes, until the void is filled. If the nozzle of a pair of bellows be closed, either by the finger or by a small valve opening outwards; and a short pipe, the lower end of which is placed in water, be secured to the opening in the under board which is covered by the clapper; then if the bellows be opened, the pressure of the atmosphere will drive the water up the pipe to fill the enlarged cavity, and by then closing the boards, the liquid will be expelled through the nozzle. Bellows thus arranged become sucking or atmospheric, and forcing pumps. When the orifice of a syringe is inserted into a vessel of water and the piston drawn up, the air having no way to enter the vacuity thus formed than by the small orifice under the surface of the liquid, presses the water before it into the body of the syringe. one, As every machine described in this book, and most of those in the next both proves and illustrates atmospheric pressure on liquids, we need not enlarge further upon it here. There are however some other particulars relating to it, which are necessary to be known: first, that its pressure is limited; and secondly, that it varies in intensity at different parts of the earth, according to their elevation above the surface of the sea. These important facts are clearly established in the accounts given of the discovery of the air's pressure, a sketch of which can scarcely be out of place here, since it was a pump that first drew the attention of modern philosophers to the subject, and which thereby became the proximate cause of a revolution in philosophical research, that will ever be considered an epoch in the history of science. Chap. 2.] Discovery of Atmospheric Pressure. 187 CHAPTER II. Discovery of atmospheric pressure-Circumstances which led to it-Galileo--Torricelli-Beautiful experiment of the latter-Controversy respecting the results-Pascal-his demonstration of the cause of the ascent of water in pumps-Invention of the air-pump-Barometer and its various applicationsIntensity of atmospheric pressure different at different parts of the earth-A knowledge of this necessary to pump-makers-The limits to which water may be raised in atmospheric pumps known to ancient pump-makers. In the year 1641, a pump-maker of Florence made an atmospheric, or what was called a sucking pump, the pipe of which extended from 50 to 60 feet above the water. When put in operation, it was of course incapable of raising any over 32 or 33 feet. Supposing this to have been occasioned by some defect in the construction, the pump was carefully examined, and being found perfect, the operation was repeated, but with the same results. After numerous trials, the superintendent of the Grand Duke's water works, according to whose directions it had been made, consulted Galileo, who was a native of the city, and then resided in it. Previous to this occurrence, it was universally supposed that water was raised in pumps by an occult power in nature, which resisted with considerable force all attempts to make a void, but which, when one was made, used the same force to fill it, by urging the next adjoining substance, if a fluid, into the vacant space. Thus in pumps, when the air was withdrawn from their upper part by the 'sucker,' nature, being thus violated, instantly forced water up the pipes. No idea was entertained by philosophers at this or any preceding period, that we know of, that this force was limited; that it would not as readily force water up a perpendicular tube, from which the air was withdrawn, 100 feet high as well as 20-to the top of a high building as well as to that of a low one. When the circumstances attending the trial of the pump at Florence were placed before Galileo, (his attention having probably never before been so closely directed to the subject) he could only reply, that nature's abhorrence to a vacuum was limited, and that it " ceased to operate above the height of 32 feet." This opinion given at the moment, it is believed was not satisfactory to himself; and his attention having now been roused, there can be no doubt that he would have discovered the real cause, had he lived, especially as he was then aware that the atmosphere did exert a definite pressure on objects on the surface of the earth. But at that period this illustrious man was totally blind, nearly 80 years of age, and within a few months of his death. The discovery is however, in some measure, due to him. It has also been supposed that he communicated his ideas on the subject to Torricelli, who lived in his family and acted as his amanuensis during the last three months of his life. It was in 1643 that Torricelli announced the great discovery that water was raised in pumps by the pressure of the air. This he established by very satisfactory experiments. The apparatus in his first one, was made in imitation of the Florentine pump. He procured a tube 60 feet long, and secured it in a perpendicular position, with its lower end in water; then having by a syringe extracted the air at its upper end, he found the water rose only 32 or 33 feet, nor could he by any effort induce it to |