angle H M C, and the base line H C, or the earth's semidiameter being known, which is nearly 4000 miles-the length of the line H M, or the distance of the moon, can be easily determined. It may be proper also to state that the farther any heavenly body is distant from the earth, the less is its parallax. Hence the parallaxes of the sun and planets are all much less than that of the moon, which is the nearest celestial body to the earth. Thus, the parallaxed of the planet P is less than that of the Moon, M, and the same principle likewise holds true with respect to all terrestrial objects. This subject may soon be rendered quite plain to the pupil, by familiar illustrations, in connection with a few instructions on the nature and properties of triangles, and the first principles of trigonometry.

I have been somewhat particular in some of the hints thrown out above, because it is of some importance that the young should have clear and impressive conceptions of every object presented to their view, in every step of their progress on this subject, and not depend merely on the assertions or the positions announced by their teachers; and because such a train of observations and experimental illustrations has seldom been attended to, in attempting to convey to the juvenile mind a popular view of the leading facts of astronomy. After the pupil has acquired a knowledge of the subjects to which I have adverted, an intelligent teacher will find little difficulty in gradually unfolding to him the doctrines and facts in relation to solar and lunar eclipses the tides the form of the planetary orbits-the nature of refractionthe divisions of time-the mensuration of the

In illustrating the principles and exhibiting the objects of astronomy, the pious and intelligent teacher will have frequent opportunities of impressing upon the minds of his pupils the most sublime ideas of the Perfections of the Creator, and of the Extent and Grandeur of his Empire, and of inspiring them with Love, Admiration, and Reverence; and such opportunities ought never to be neglected. When descanting on the number and magnificence of the celestial world, he may very appropriately take occasion to impress them with the idea of the littleness of this earth, and its comparative insignificance, when placed in competition with the numerous and more resplendent worlds and systems which compose the universe; and, consequently, with the folly and madness of ambition, and of all those warlike schemes and ferocious contentions, of which our world has been the melancholy theatre. He may occasionally expatiate a little on the folly of pride, and its inconsistency with the character and circumstances of man, when we consider his comparative ignorance, and the low station which he holds in the scale of creation-and the reasonableness of cultivating a spirit of humility in the presence of that Almighty Being whose "glory is above the heavens," and "whose kingdom ruleth over all," when we consider, that, when compared with the myriads of more exalted intelligences that people the universe, we are only like a few atoms in the immensity of space. He may direct their attention to the infinitely diversified scenes of grandeur and felicity which the universe must contain, since its range is so extensive and its objects so magnificent; and to the evidence which these facts afford, that the Creator has it in his power to gratify his rational offspring with new objects, and new sources of enjoyment, during every period of infinite duration.—In short, he may excite them, from such considerations, to aspire after that more glorious state of existence where the works of Omnipotence will be more fully unfolded, and to cultivate those holy principles and dispositions which will qualify them for mingling in the society and engaging in the employments of the heavenly world. Such instructions, when amalgamated with Christian views and motives, could not fail of producing a beneficial impression on the susceptible hearts of the young, which might, in some measure, influence their conduct and train of thought through all the remaining periods of their lives.*

* The most celebrated writers on Astronomy are Long, Ferguson, La Caille, Martin, O. Gregory,

Chemistry.

The object of Natural and Experimental Philosophy is to investigate the phenomena of the material world, in order to discover their causes, and the laws by which the Almighty directs the movements of the universe ; and to apply the observations and discoveries we make to useful purposes in human life, and to expand our views of the perfections and operations of the Creator. This department of study has generally been divided into the following subordinate branches, Mechanics, Hydrostatics, Hydraulics, Pneumatics, Meteorology, Acoustics, Optics, Electricity, Galvanism, and Magnetism. This is a subject, the popular and experimental parts of which may be rendered highly entertaining and instructive to the minds of the young. But, however important the subject in all its branches may be to the regular scientific student, it would be inexpedient to attempt conveying more than a general view of the more popular parts of it to young persons from the age of ten to the age of fourteen, although many of the experiments connected with it may, with propriety, be exhibited even to children of an earlier age, in order to excite a taste for the study of natural science. Experimental illustrations of the subjects of Natural Philosophy sometimes require an extensive apparatus, which cannot be procured but at a considerable expense; but there are many interesting experiments, illustrative of scientific principles and facts, which can be performed with very simple apparatus, and at little expense; and all that I propose, under this article, is to suggest a few of those experiments which almost every teacher may have it in his power to perform.

In the department of Mechanics,-illustrations might be given of the mechanical powers, which are generally arranged under the heads

Vince, Herschel, Robison, La Lande, La Piace, Biot, and various others. Popular works on this subject, which may be put into the hands of young persons, are such as the following:-Ferguson's "Gentleman and Lady's Astronomy"- Martin's "Gentleman and Lady's Philosophy," vol. i.Bonnycastle's "Introduction to Astronomy"Mrs. Brian's "Astronomy"-"The Wonders of the Heavens"-Gregory's "Astronomical Les sons," &c. But none of these works are adapted to the purpose of teaching. The best treatise of this kind I have seen, calculated to be a text book for an intelligent teacher. is a work entitled "The Geography of the Heavens," by Elijah H. Burrit, A. M., lately published at Hartford, State of Connecticut. This volume comprises 342 closely printed pages, large 18mo., and several appropriate wood-cuts. It contains a very full and lucid description of all the particulars respecting the different constellations and principal stars, the general principles of astronomy, the facts connected with the solar system. problems, astronomical tables, and almost every thing that can be deemed inte

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inclined plane, the wedge, and the screw. A simple apparatus for illustrating these powers could easily be constructed by an ingenious mechanic, at a trifling expense, and might be rendered conducive both to the entertainment and instruction of the young. In particular, the nature and power of the lever, and the principle on which it acts, should be minutely explained, by experimental illustrations, and by showing its effects in the common operations of life. A long bar of iron or hard wood might be erected on a steady fulcrum, and placed in the area adjacent to the school, which might serve both for amusement and for illustrating the power of the lever. This bar might be divided into feet or half feet, or any convenient number of equal parts, and so constructed that any of those parts might be placed upon the fulcrum. By such a lever the different powers to be applied at distances from the fulcrum, when a weight is to be raised, might be familiarly illustrated. A seat or swing might be fixed at one end of the beam, on which a boy might sit, while some of his companions, towards the other end, applied different powers or weights at different distances from the fulcrum, as a counterpoise; which would suggest various calculations 'respecting the powers requisite to be applied in any given case, according to the distance from the point of support. It will tend to excite their interest in this subject, when they are informed that scissors, pincers, snuffers, oars, the balance, the see-saw, doors turning on hinges, the rudders of ships, cutting knives fixed at one end, and the bones of the arm, are all so many different kinds of levers; and that the operations of quarrying stones, raising great weights, poking the fire, rowing a boat, digging the ground, and such like, are all performed on the principle of this mechanical power. Similar contrivances might be adopted for illustrating the wheel and axle and other

resting to the general student. Every page contains Questions, as exercises for the judgment of the pupil. It is accompanied by a large and beautiful Atlas, 16 inches by 14, containing 7 Planispheres or Maps of the Heavens: 1. The visible heavens in October, November, and December. 2. Do. in January, February, and March. 3. Do. in April, May, and June. 4. Do. in July, August, and September. 5 The visible heavens in the North Polar Regions for each month of the year. 6. Do. in the South Polar Regions. 7. Planisphere of the whole heavens on Mercator's projection. "The first four maps are so constructed, that the pupil in using them must suppose himself to face the south, and to hold them directly over head. in such a manner that the top of the map should be towards the north, and the bottom towards the south." In the construction of these maps, and in the composition of the work, the latest discoveries have been carefully inserted. This work, since its first publication in 1833, has had an extensive sale in the United States, and been introduced into many respectable seminaries.

tubes are filled with water. To show the different quantities and velocities of water spouting at different distances from the surface of a reservoir, such a vessel as that represented, Fig. 4, page 118, may be used. The water will issue from the orifice at C with greater velocity, and consequently in greater quantity than at B or A; if the orifice C be four times as deep below the surface as the orifice A, it will discharge twice as much water in a given time as A, because 2 is the square root of 4; if the orifice B be in the centre of the column of water, it will project the water to the greatest horizontal distance. The vessel here represented may be made either of wood or of tin-plate, and if a bent tube be inserted at D, and the holes A B C shut up, it may serve to exhibit a jet d'eau The cup of Tantaulus, the fountain at command, the hydraulic dancers and divers, and other entertaining devices might also be exhibited, and accompanied with explanations of the principles on which they act. By such means, several of the leading principles of hydrostatics might be easily impressed upon the youthful mind, and would doubtless be found of practical utility in future life, provided the teacher is careful to show, by familiar examples, how they explain many of the phenomena of nature and operations of art.

The science of Pneumatics affords scope for many curious discussions and experiments respecting the air and atmospherical phenomena, which may be rendered interesting to the young. In illustrating the pressure, elasticity, and other properties of the atmosphere, the assistance of the air-pump, with its usual apparatus is highly desirable; as, without it, some of the most interesting experiments on this subject cannot be performed. But where this instrument, on account of its expense, cannot be procured, various useful and entertaining experiments may be exhibited by means of a simple apparatus which almost every one can procure. For example, the pressure of the atmosphere may be proved to the conviction of every one by such simple experiments as the following:-The common experiment of filling a wine-glass with water, covering its mouth with a piece of paper, and then inverting it, is quite decisive of the atmospheric pressure; for the paper underneath, instead of being convex by the pressure of the water within, is concave, by the pressure of the atmosphere from without; and no other cause can be assigned why the water is supported in the glass. Another simple experiment, where no paper is employed, proves the same fact: Take a glass tube, two or three feet long, with a narrow bore; put one end of it into a vessel of water, put your mouth to the other end, and make a deep inspiration till

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the air is drawn out of the tube, when the water will rush to the top of the tube; then place your thumb on the top to prevent the access of air from above, and when the other end of the tube is taken out of the water, the column of water will be suspended in the tube by the atmospheric pressure, although the lower end of it is open. When the air is sucked out of the tube, a vacuuin is produced, and the external air, pressing upon the surface of the water in the vessel, forces it to the top of the tube; the thumb being applied prevents the air pressing the water down, and the atmospheric pressure on the bottom prevents the water from running out. The same fact is proved by the following experiment: Let a piece of burning paper be put into a wine-glass, so as to rarify or exhaust the air, and while it is still burning, press the palm of the hand against the mouth of the glass, when it will adhere with a considerable degree of force, by the pressure of the atme sphere on the bottom and sides of the glass, This experiment may be varied as follows Pour a certain quantity of water into a saucer; invert a wine-glass over a piece of burning paper or burning brandy, and, after holding it a short time in the flame, place it in the saucer, when the water will rush up into the glass in consequence of the atmospheric pressure, as it did in the glass tube when it was exhausted of its air by suction. These and similar experiments, which every one may perform, are as decisive proofs of the atmospheric pressure as those which are performed by means of the air-pump. Such experiments, when conducted by intelligent teachers, may easily be applied to the explanation of the causes of certain natural and artificial processes, such as the firm adherence of two polished surfaces-the action of a boy's sucker in lifting large stones-the operation of cupping-the process of a child's sucking its mother's breast-the effects produced by cements-the rise of water in pumps--the firm adhesion of snails and shell-fish to rocks and stones-the action of syphons-what is termed suction, as when we take a draught of water from a running stream-the fact, that a cask will not run, in certain cases, unless an opening is made in its top-and many similar processes, some of which will be found of considerable practical utility.

The elasticity of the air may be proved by such experiments as these:-Take a bladder, and fill it with air by blowing into it, and then apply a force to the sides of it, so as to compress . it into a smaller space; when the force is removed, it immediately expands and fills the same space as before. This experiment proves, not only the elasticity of air, but that, though invisible, it is as much a material

substance as wood or iron; for no force can bring the sides together, without breaking the bladder, although the parts of an empty bladder may be squeezed into any shape. The same thing is proved by the following experiment :-Open a pair of common bellows, and then stop the nozle, so that no air can rush out-and no force whatever can bring the parts together, without bursting the leather, or unstopping the nozle. That heat increases the elasticity of air, may be shown, by placing before a strong fire a bladder with a small quantity of air, when the small portion of air will expand, till the bladder appear quite full and ready to burst. These experiments may be applied to the explanation of such phenomena as the following:-Why the compressed air between the liquid and the cork, in a bottle of beer or ale, bursts forth in the form of froth when the cork is drawn-why fishes, in consequence of their air-bladders, are enabled to rise and sink in the water-and why the carcass of a man that has been drowned, in a few days rises and floats on the surface for a short time, and then sinks to rise no more. The compressibility of air may be shown, by taking a glass tube which is open only at one end, and of course full of air, and plunging the open end into a vessel of water, when the water will be seen to have risen to a small height, near the bottom of the tube, which proves that the air which filled the whole length of the tube is compressed by the water, into a smaller space. In a similar way the principle of the diving-bell may be illustrated. Let A B, Fig. 1, represent a large tumbler or drinking glass, which may be nearly filled with water. Place a piece of cork on the surface of the water, and over the cork an ale-glass C D, with its mouth downwards, then push the glass perpendicularly down towards the bottom of the tumbler, and

A

Fig. 1. C

the cork will appear swimming a little above the 'bottom; plainly indicating that there is no water above it in the ale-glass, which is prevented from entering by the resistance of the air within. The wa B ter in the tumbler

may represent the water of a river or of the sea; the ale-glass may represent the divingbell, in which a person may sit

with safety in the depths of the sea without touching the water, provided fresh air be supplied. A small quantity of water will be found to have entered the ale-glass, and the deeper it is plunged in any vessel the higher will the water rise within it. At the depth of 33 feet, where the pressure of the atmosphere is doubled, a diving-bell will be half filled with water-at the depth of 66 feet, it will be two-thirds filled-at the depth of 99 feet, it will be three-fourths filled, and so on in proportion to the depth; which shows the propriety of having this vessel in the form of a bell, that the perpendicular height of the water may be as little as possible. The following simple experiment illustrates the pressure of the atmosphere in a mode somewhat different from those already stated. Procure a tin vessel about six or seven inches long, and three in diameter, having its mouth about a quarter of an inch wide, as E F, Fig. 2. In its bottom make a number of small holes, about the diameter of a common sewingneedle. Plunge this vessel in water, and when full cork it up, so that no air can enter at the top. So long as it remains corked, no water will run out-the pressure of the atmosphere at the bottom preventing it; but as soon as it is uncorked, the water will issue from the small holes in the bottom, by the pressure of the air from above. The same experiment may be made by means of a tube, Fig. 2. Fig. 3

seven or eight inches long, and about threefourths of an inch diameter, having two or three small holes in its bottom; and another tube, G H, Fig. 3, of the same dimensions, having a small hole in each side, I K, will illustrate the lateral pressure of the atmosphere

the water being retained when it is corked, and running out when the cork is removed. It will likewise illustrate the lateral pressure of water and other liquids.

Several amusing experiments may also be performed by means of syphons, when concealed in drinking-cups and other vessels;