on the lunar disk. The solar spots may be viewed 14 feet, Saturn; and, at 95 inches, or about 8 feet with ease, by interposing a colored glass between from the sun's ball, place one to represent Herschel. the eye and the image of the sun; but, in looking This will convey a pretty correct idea of the prothrough the telescope in the ordinary way, they can portional distances from the sun of the principal be perceived by only one individual at a time. In primary planets. The distances of Ceres, Pallas, order to exhibit them to a company of 30 or 40 per- Juno, and Vesta, might likewise be represented, if sons at once, the image of the sun may be thrown judged expedient; but as their orbits are more econ a white wall or screen. I have generally exhi-centric than those of the other planets, and some bited them in the following manner. To a 3 feet of them cross each other, they cannot be accurately Achromatic telescope, I apply a diagonal eye-piece represented. When orreries or telescopes cannot which has a plain metallic speculum placed at half be procured for exhibiting the celestial motions and a right angle to the axis of the telescope. By this phenomena to which I have alluded, some of these eye-piece, after the room has been darkened as objects, such as the rings of Saturn, the belts and much as possible, the image of the sun and his spots moons of Jupiter, the phases of Venus, the Moon, is thrown upon the roof of the apartment, which and some of the constellations, may be represented forms a beautiful circle of light, and exhibits all the in a dark room by means of the phantasmagoria. spots which then happen to diversify his surface. But the representations made by this instrument His apparent diurnal motion is also represented, form but a rude and paltry substitute for the exhialong with the motions of any thin fleeces of clouds bitions presented by the orrery and the telescope, which may happen to cross his disk. In this way, and need never be resorted to, except for amusetoo, the proportional magnitudes of the spots may ment, where these instruments can be obtained. be measured, and compared with the diameter of the sun, and, of course, their real magnitudes ascertained.

It might next be expedient to communicate to the pupil an idea of the nature of a parallax, to prepare him for understanding the mode by which the distances and magnitudes of the heavenly bodies are ascertained. This might be done by fixing a pole or staff, with a pointed top, in a garden or large area, opposite a wall or hedge, F G, Fig. 1, and, desiring one of the pupils to take his station at A, and another at B, and to direct their eyes to the points on the wall which appear in a line with the top of the pole, when the one stationed at A will Fig. 1.

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In illustrating the phenomena of the planetary system by means of orreries, planetariums, and lunariums, great care should be taken to guard the young against the false and imperfect conceptions of the magnitudes and distances of the planets, which such instruments have a tendency to convey. No orrery, of a portable size, can represent, at the same time, both the proportional distances and relative magnitudes of the different planets: Even those large machines designated Eidouraniums and Transparent Orreries afford no correct views of these particulars; and some of them convey very erroneous and distorted conceptions of the relations of the solar system, where it is the chief design to dazzle the eye with a splendid show. In some of these exhibitions I have seen the stars represented as if they had been scattered through different parts of the planetary system.-An orrery representing d the proportional distances and magnitudes of the sun and planets would require to be more than three u miles in diameter; and, even on this scale, Jupiter u would be less than 3 inches diameter, the Earth cer a quarter of an inch, or about the size of a small pea, and Mercury only about the dimensions of the t head of a small pin, while the sun would require to be represented by a ball 30 inches in diameterin which case all the planets would be invisible from the centre of the system. To correct, in some perceive it to coincide with the point C, and the we measure, the erroneous ideas which a common or other stationed at B will perceive it at D. They rery is apt to convey, the magnitudes and distances may be told that CD is the parallax, or the dif should be separately represented. Suppose a celes-ference of the apparent place of the pole P, when tial globe, 18 inches in diameter, to represent the Sun, Jupiter will be represented by a ball about 14 "inch diameter, Saturn by one of 13 inch, Herschel by one about inch, the Earth by a ball of inch, or somewhat less than a small pea, Venus by ta ball of nearly the same size, Mars by a globule of about inch, Mercury by a globule of 151 and the Moon by a still smaller globule of inch in diameter. These three last might be represented Joby three different sizes of pin-heads. When balls of these sizes are placed adjacent to an 18-inch globe, and compared with it, an impressive idea is conveyed of the astonishing magnitude of the sun, which is 500 times greater than all the planets, satel7 lites, and comets, taken together. The proportional distances may be represented as follows. At one Mend of a table 9 feet in length, fix a ball upon a pillar to represent the sun; at 2 inches from the sun's ball, place another to represent Mercury; at 3 inches, Venus; at 5 inches, the Earth; at 7 inches, Mars; at 25 inches, Jupiter; at 474 inches, or about MA no149* tul

viewed from the positions A and B, which is measured by the angle CPD; and that, if the distance between A and B were measured, and the number of degrees or minutes in the angle C P D or APB of the stations can be easily determined. This ascertained, the distance between the pole and any may be easily applied to the case of the heavenly bodies by means of such a diagram as Fig. 2, where HIK represents the Earth, M the Moon, P a planet, and S T a quadrant of the starry heavens. It is evident, that, if the moon be viewed from the surface of the earth at H, she will appear in the heavens at the point a; but if she be viewed from the centre C, she will be seen at the point b, the angle a Mb being the angle of parallax. This angle being found, which is the same as the 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.

I have been somewhat particular in some of the | stances of man, when we consider his comparative hints thrown out above, because it is of some import- ignorance, and the low station which he holds in the ance that the young should have clear and impres- scale of creation-and the reasonableness of cultisive conceptions of every object presented to their vating a spirit of humility in the presence of that Alview, in every step of their progress on this subject, mighty Being whose "glory is above the heavens," and not depend merely on the assertions or the po- and whose kingdom ruleth over all," when we sitions announced by their teachers; and because consider, that, when compared with the myriads of such a train of observations and experimental illus- more exalted intelligences that people the universe, trations has seldom been attended to, in attempting we are only like a few atoms in the immensity of to convey to the juvenile mind a popular view of the space. He may direct their attention to the infiniteleading facts of astronomy. After the pupil has ly diversified scenes of grandeur and felicity which acquired a knowledge of the subjects to which I have the universe must contain, since its range is so exadverted, an intelligent teacher will find little diffi- tensive and its objects so magnificent; and to the culty in gradually unfolding to him the doctrines evidence which these facts afford, that the Creator and facts in relation to solar and lunar eclipses the has it in his power to gratify his rational offspring tides the form of the planetary orbits-the nature with new objects, and new sources of enjoyment, of refraction-the divisions of time-the mensura- during every period of infinite duration. In short, tion of the earth-centrifugal and centripetal forces-- he may excite them, from such considerations, to asthe circles of the celestial sphere-and various other pire after that more glorious state of existence where particulars connected with astronomical science. the works of Omnipotence will be more fully unIn illustrating the principles and exhibiting the ob-folded, and to cultivate those holy principles and jects of astronomy, the pious and intelligent teacher dispositions which will qualify them for mingling will have frequent opportunities of impressing upon in the society and engaging in the employments of the minds of his pupils the most sublime ideas of the heavenly world. Such instructions, when amalthe Perfections of the Creator, and of the Extent gamated with Christian views and motives, could and Grandeur of his Empire, and of inspiring them not fail of producing a beneficial impression on the with Love, Admiration, and Reverence; and such susceptible hearts of the young, which might, in opportunities ought never to be neglected. When some measure, influence their conduct and train of descanting on the number and magnificence of the thought through all the remaining periods of their celestial worlds, he may very appropriately take oc- lives.* casion 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 circum

* The most celebrated writers on Astronomy are Long, Ferguson, La Caille, Martin, O. Gregory, Vince, Herschel, Robison, La Lande, La Place, 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. 1Bonnycastle's "Introduction to Astronomy" Mrs.

SECTION IX.-Experimental Philosophy and
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, Elec-school, which might serve both for amusement and tricity, 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 of the lever, the pulley, the wheel and axis, the 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 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 different 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 Bryan's "Astronomy"-" The Wonders of the adopted for illustrating the wheel and axle, and other Heavens"-Gregory's "Astronomical Lessons," &c. powers. A knowledge of the mechanical powers But none of these works is adapted to the purpose may be useful to every individual, whatever may of teaching. The best treatise of this kind I have be his trade or profession in future life, but particuseen, calculated to be a text-book for an intelligent larly to those who may afterwards engage in the teacher, is a work entitled "The Geography of the arts of carpentry, architecture, mining, engineering, Heavens," by Elijah H. Burritt, A. M., lately pub- and other operations where a knowledge of the melished at Hartford, State of Connecticut. This vo- chanical powers is essentially requisite; and the imlume comprises 342 closely printed pages, large pressions made upon their minds in early life by fa18mo, and several appropriate wood-cuts. It con- miliar illustrations of these powers, would tend to tains a very full and lucid description of all the par-facilitate their study of such subjects when they beticulars 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 interesting 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.

came the more particular objects of their attention.

The fundamental principles of Hydrostatics and Hydraulics might be familiarly illustrated by a variety of simple experiments, some of which might be rendered extremely amusing. That fluids press in all directions-that their pressure is in proportion to their perpendicular height-that a small quantity of a fluid may be made to counterpoise any quantity, however great-that a fluid specifically lighter than another will float upon its surface-that the surface of all fluids which communicate with each other will be on the same level-that the velocity with which water spouts from holes in the side of a vessel, is in proportion to the square root of the distance of the holes below the surface of the water. These, and similar positions, along with the principles on which syphons, jets, and artificial fountains act, can be illustrated with an apparatus which every intelligent teacher, if he has the least share of mechanical ingenuity, can easily construct for himself, with the assistance of glass vessels, which are to be found in almost every family. To show that water will find its level, and rise to the same height in tubes which have a communication, an instrument similar to the following, Fig. 1. may be constructed: A B and ED are two tubes which have a communication with each other by means of the tube BD;

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 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 vacuum 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 atmosphere 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 wineglass over a piece of burning paper, or burning brandy, and, after hoiding 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 airpump. 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 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,

The water in the tumbler may represent the water of a river or of the sea; the ale-glass may represent the diving-bell, 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 twothirds filled-at the depth of 99 feet, it will be threefourths 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