but as soon as it is uncorked, the water will issue from the small holes in the bottom, by the pressure 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 sewing-needle.of the air from above. The same experiment may Fig. 2. E F Fig. 3. G K be made by means of a tube, seven or eight inches long, and about three-fourths 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; and the utility of the principle on which they act may be illustrated in certain practical operations. For example, their use may be shown in conveying water over a rising ground. In Fig. 4, let M represent a pond or pool of water, in a quarry or other situation, which is wished to be drained, and where there is no declivity or lower ground adjacent to which the water can be conveyed-it may be carried over the rising ground M N, by means of the syphon M N L; provided the perpendicular elevation N P, above the level of the pool M, does not exceed thirty-two feet, for to that height only will the water rise in the Fig. 4. empronta els matter ir du mobed H 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; of conveying water from a fountain at R, along a hollow or valley to a house, S, at the same height on the other side of the valley; and however deep or broad the valley may be, the water may in this manner be conveyed, provided the syphon is sufficiently strong near its lower parts to sustain the perpendicular pressure of the water. sion of air. Procure a common Florence flask, FG, Fig. 6, and pour into it a large wine-glassfull of water; then take a tube, I H, bent at the top, H, like a small syphon, and fasten it air-tight into the mouth of the flask, I, so that its bottom may be immersed in the water at K, but not touching the bottom of the flask. Then immerse the flask into a vessel of The following simple and interesting experiment very hot water, when, in consequence of the expanmight be exhibited to show the effects of the expansion of the air in the flask, the water at K will be instruments are very expensive. I shall therefore state only a few simple exhibitions and experiments which can be made at a trifling expense. Before the teacher can illustrate any of the principles of this science by experiment, it will be requisite that he provide himself with a few convex lenses, some of short and others of pretty long focal distances. For example, double or plano-convex glasses, & inch, 1 inch, 3 and 4 inches, focal distance, which may be made to illustrate the construction of a compound microscope, as I have elsewhere shown in my work, "On the improvement of Society." Also lenses, from 3 to 6 or 8 feet focus, to illustrate the construction of a telescope, and the nature of a camera obscura; and two or three concave mirrors for illustrating some of the phenomena of reflection. The principle on which a compound microscope, a salar microscope, and a magic lantern or phantasmagoria, are constructed, may be shown by one easy experiment. Let A, Fig. 1, represent a convex glass, suppose six inches focal distance, and B the flame of a candle. Hold the glass, A, at a little more than six inches from the candle, and on an opposite wall K The flask may then be again immersed in the hot water, when the water at its bottom will be thrown up into the wine-glass as before, and the operations may be repeated as often as judged expedient. This experiment, when dexterously performed, seldom fails to produce a pleasing effect upon the spectators, especially when the water is tinged with a red color, by means of the sulphuric or any other acid dropped into an infusion of red cabbage.* The science of Optics affords scope for many delightful and interesting experiments; but some of its In arranging and performing such simple experiments as those above stated, it is expedient that the teacher or operator should know how to cut phials and glass tubes, and to form syphons. The neck of a common phial may be cut off, so as to form a tube, by slightly indenting a portion of the circumference with the sharp edge of a common file, and then, with the point of a hot iron, beginning at the indentation, go round the circumference of the phial, and the head will at once be separated from the body. Otherwise, tie a thread which has been steeped in turpentine or spirits of wine firmly round the mouth of the phial, then set fire to it, and the operation is performed. In the same manner, long glass tubes may be cut into any lengths. If the tubes be of a small diameter, it is only requisite to indent them with a file at the point where they are intended to be cut, and then, holding the one end of the tube in the left hand, give a blow with the right on the other end, and the tube will snap asunder.-To bend a glass tube into the form of a syphon: Put the tube through the bars of a common grate, when the fire is burning clear; let the part of the tube which is to be bent be in the centre or hottest part of the fire; take hold of the tube at both ends, and when it be gins to melt near the middle, gently bend it, with both hands, in the form which is wanted, and then remove it from the fire. A little experience will render such operations quite easy and efficient for the purpose intended. If a small bend only at one end of the tube is required, that end may be put into the fire till it begin to melt, then take hold of it gently with a pair of tongs, and bend it in the form required with the right hand. Fig. 1. will be formed a large magnified image of the candle, C E D. This image will be inverted, and larger than the flame of the candle in proportion as the distance A E, from the glass to the wall, exceeds the distance A B, from the glass to the candle. Suppose the distance A B to be exactly 6 inches, and the distance A E to be 7 feet or 84 inches, then the image of the candle will be magnified in the proportion of 6 to 84, or 14 times. In this experiment the candle represents the object to be magnified in a compound microscope, A the object-glass, and CD the image formed by the lens, which is magnified a second time by the eye-glass of the microscope. In reference to the solar microscope, the candle represents the small object to be magnified, and C D its magnified image on a white wall or screen; and in reference to the magic lantern, or phantasmagoria, the candle represents the figures painted on the sliders, A the convex lens which throws the image of the figures on a screen, and C D the magnified image of the painted figures. In all these instruments, the principle on which the objects are magnified is precisely the same; the size of the image is always in proportion to its distance from the lens by which it is formed; but as the image is enlarged it becomes less brilliant and distinct, and therefore there is a proper medium which must be fixed upon the east; and if it be turned round another quadrant, till it be directly opposite to its first position, and the eye applied from below, the object or landscape will appear as if suspended in the atmosphere above us. Such experiments, when accompanied with proper diagrams, and an explanation of optical principles, may easily be rendered both entertaining and instructive. Fig. 3. K as to the distance between the lens and the screen on which the image is thrown; but a skilful teacher will always know how to modify such circumstances. The nature of a telescope and of the camera obscura may be illustrated as follows:-Fix a lens of 4, 5, or 6 feet focus, in a hole made in a windowshutter; darken the room, so that no light can enter but through the lens. If its focal distance be 5 feet, or 60 inches, a white screen placed at that distance A camera obscura, on a larger scale, and on a will receive the image of the objects without, oppo- different plan from that alluded to above, might be site the glass, where they will be beautifully depict-erected on the top of every school-house, which is ed in all their forms, colors, and motions, in an in- constructed with a flat roof, as formerly suggested. verted position, forming a kind of living picture. Fig. 3 contains a representation of a wooden buildThis exhibition never fails to excite the admiration of the young. If now, a lens about 2 inches focus be placed 2 inches beyond the image thus formed, and the screen removed-in looking through this lens, the objects will appear magnified in the proportion of 2 inches to 60, that is, 30 times; and as the image was inverted, so the object, as seen through the glass, will appear as if turned upside down.This is perhaps one of the best modes of explaining the principle of a refracting telescope, and the reason why the object appears inverted, when viewed with a single eye-glass. The same thing may be partly shown by a common telescope. Having taken out all the eye-glasses, except the one next the eye, adjust the telescope to distinct vision, and all the objects seen through it will appear as if turned upside down. The manner in which the image is reversed by the other eye-glasses, and the object made to appear upright, might then be explained. Objects might likewise be exhibited through a telescope, as appearing in different positions and directions. This is effected by means of a diagonal eye-piece, which is constructed in the following manner: Let AB, Fig. 2, represent a convex glass about 2 inches focal distance; CD a plain metallic speculum, of an oval form, well polished, and placed at half a right angle to the axis of the tube; and E F, another convex lens, 2 inches focus. The centre of the speculum may be about 1 inch from A B, and about inch from EF. The rays proceeding from the lens A B, and falling from the speculum, are reflected in a perpendicular direction to the lens E F, where they enter the eye, which looks down upon the object through the side of the tube. When this eye-piece is applied to a telescope, with the lens E F on the upper part of it, we look down upon the object as if it were under our feet. If we turn the eye-piece round in its socket a quarter of a circle towards the left, an object directly before us in the south will appear as if it were in the west, and turned upside down. If, from this position, it is turned round a semicircle towards the right, and the eye applied, the same object will appear as if it were situated in A lens is a round piece of glass, ground either concave or convex. All lenses that magnify objects are convex, or thicker in the middle than at the edge, such as common magnifiers, reading-glasses, and the glasses used in microscopes and telescopes, except the Galilean perspective, in which the eye-glass is concave. H T ing, on the top of which is a large convex lens HI, about 10 or 12 feet focal distance. At half a right angle to this lens is a plain speculum, by which the rays of light from the objects O are reflected downwards through the lens, which forms a picture of all the objects before the speculum, on a round white table, T, in all their colors, motions, and proportions. If the speculum be made to revolve, the whole of the surrounding landscape may be successively depicted on the table. When the lens is of a long focal distance, as from 10 to 15 or 20 feet, it produces a pretty powerful telescopical effect, so that objects may be distinctly perceived at a considerable distance, and individuals recognised on the picture at the distance of a mile or more. Wherever there are objects in motion, such as ships sailing, birds flying, smoke ascending, crowds of people moving to and fro, or boys and girls engaged in their amusements; this exhibition always affords a high degree of satisfaction. It might occasionally be used, not only as an illustration of optical principles, but also as a reward for diligence and good behavior. In connection with the above, representations might be given of natural and artificial objects as exhibited by the phantasmagoria. Discarding the ridiculous and childish figures which were formerly used in the common magic lanterns, opticians have now constructed sliders which exhibit representations of the telescopic appearances of the heavenly bodies, the different constellations, the motions of the earth and moon, and various objects connected with botany, mineralogy, and zoology; and such objects, when exhibited in this manner, are calculated to produce both instruction and amusement. The solar microscope in particular, (or the oxy-hydrogen, if it can be procured,) should be occasionally exhibited to the young, to convey to them some ideas of the wonderful minuteness of the atoms of matter, and the admirable mechanism displayed in the structure of vegetables and the bodies of animals, particularly in those myriads of animalcula which | collects the rays into a focus before it, so as to act are invisible to the unassisted eye. Such animal- as a powerful burning glass, and in this way a hole culæ may be procured almost at any season, but may be burned in a thin board. 3. When hung at particularly during the summer months, by infusing an elevation of about 5 feet, and a person placed opin separate open vessels, small bits of grass or hay, posite to it, at 6 or 7 feet distant, he will see his imleaves of flowers, or other vegetable substances, age hanging in the air in an inverted position, bewhen, after a week or ten days, animalculæ of dif- tween him and the mirror, and if he approach a litferent kinds, according to the nature of the substan- tle nearer the mirror, and hold out his hand towards ces infused, will be perceived in vast numbers, by it, the image will appear to do the same, as if about the aid of the microscope, in every drop of the infu- to shake hands, and if he stretch his hand still sion. A compound microscope is perhaps as good nearer the mirror, the hand of his image will apan instrument as any other for giving a steady and pear to pass by his hand, and approach nearer his satisfactory view of such objects; and the only ob- body. 4. Such a mirror is of use in explaining the jection to its use for a school is, that only one indi- construction of a reflecting telescope. When it is vidual can see the object at a time. When a teacher held opposite to a window, the image of the sash is not furnished with an instrument of this kind fit- and of the objects without the window will be seen ted up in the usual way, he may, with little trouble, depicted in its focus on a piece of white paper held construct a compound microscope, by means of the between it and the window which represents the eye-piece of a common pocket achromatic telescope, manner in which the first image is formed by the which may be purchased for one guinea, or less.- great mirror of a reflecting telescope;-and the The eye-pieces of such telescopes contain four glas- manner in which the small speculum of a Gregorises arranged on a principle somewhat similar to that an reflector forms the second image, may be shown of the glasses of a compound microscope. If we by holding the mirror at a little more than its focal screw off one of these eye-pieces, and look through distance behind a candle, and throwing its magniit in the usual way, holding the object end about a fied image upon an opposite wall, in the same way quarter of an inch distant from any small object, as the lens, fig. 1, p. 87, by refraction, produced the such as the letters of a printed book, it will appear enlarged image CD. 5. If a bright fire be made in magnified about ten or twelve times in length and a large room, and a very smooth, well-polished mabreadth; remove from the tube the third glass from hogany table be placed at a considerable distance the eye, which is the second from the object, and near the wall, and the concave mirror so placed look through it in the same manner, holding it more that the light of the fire may be reflected from the than an inch distant from the object, and it will ap- mirror to its focus on the table-a person standing pear magnified more than twenty times in diameter, at a distance toward the fire, but not directly in the or above 400 times in surface. If, by means of small line between the mirror and the fire, will see an impasteboard tubes, or any other contrivance, we at age of the fire upon the table, large and erect, as if tach the glass that was taken out to the outside of the table had been set on fire. the object-glass of the eye-piece, so as to be nearly close to it, we shall have a magnifying power of nearly forty times; or, if we substitute for these two object-glasses a single glass of about a half-inch focal distance, we shall form a pretty good compound microscope, magnifying above forty times in diameter, and 1600 times in surface, which will afford very pleasing views of various objects in the animal and vegetable kingdoms. The magnifying powers now stated will differ somewhat in different eyepieces, according to their lengths and the focal distances of the glasses of which they are composed.The tube of the eye-piece thus arranged, may be occasionally fitted into a pasteboard tube supported by three pillars, in which may be moved up or down for adjusting it to distinct vision, and the object placed underneath and properly illuminated. These hints are suggested, on the score of economy, for those who have no regular microscopic appara tus. Various illusions and deceptions have been produced by means of concave mirrors. Pagan priests are supposed to have rekindled the Vestal fire by this instrument; and with the same instrument, on a large scale, Archimedes is reported to have burned the Roman fleet. When the mirror is concealed from the view of a spectator by certain contrivances, he may be easily deceived and tantalized with a shadow instead of a substance. He may be made to see a vessel half full of water inverted in the air without losing a drop of its contents. He may be desired to grasp what appears a beautiful flower, and, when he attempts to touch it, it vanishes into air, or a death's head appears to snap at his fingers. He may be made to behold a terrific spectre suddenly starting up before him, or a person with a drawn sword, as if about to run him through. An exhibition of this kind was some time ago brought before the public, which was effected by a concave mirror. A man being placed with his head downVarious amusing experiments besides the above wards, in the focus of the mirror, an erect image of might be exhibited to the young, such as the optical him was exhibited, while his real person was conparadox, an instrument through which objects may cealed, and the place of the mirror darkened; the be seen, although a board or other opaque body be spectators were then directed to take a plate of fruit interposed between the eye and the objects-the from his hand, which in an instant, was dexterously prism, which, in a dark room, separates the primary changed for a dagger or some other deadly weapon. colors of the solar rays-the multiplying glass, It may not be improper occasionally to exhibit such which makes one object appear as if there were deceptions to the young, and leave them for some ten, twenty, or thirty-the burning glass, which, by time to ruminate upon them till the proper explanameans of the sun's rays, sets on fire dark colored tions be given, in order to induce them to use their paper, wood, and other inflammable substances-rational powers in reflecting on the subject, and parand optical illusions produced by the various refractions, and reflections of light in water, combinations of plane mirrors, and by concave speculums. A concave mirror, about 5 or 6 inches in diameter, and 10 or 12 inches focus, which may be procured for about half-a-guinea or 15 shillings, is of great utility for a variety of exhibitions. 1. When held at nearly its focal distance from one's face, it represents it as magnified to a monstrous size. 2. When held in the solar rays, directly opposite the sun, it ticularly to teach them to investigate the causes of every appearance that may seem mysterious or inexplicable, and not to ascribe to occult or supernatural causes what may be explained by an investigation of the established laws of nature; and to guard them against drawing rash or unfounded conclusions from any subject or phenomenon which they have not thoroughly explored, or do not fully comprehend. Having enlarged much farther than I originally SECTION X.-Mathematics. intended on the preceeding departments of Natural | nation of the rationale of each experiment. Griffin's Philosophy, I have no space left for suggesting any Recreations in Chemistry; Thomson's, Turner's, hints in relation to electricity, galvanism, and mag- Parkes', Graham's and Donovan's treaties, or any netism. If the teacher is possessed of an electrical other modern system of chemistry, may also be conmachine and a galvanic apparatus, and is acquaint- sulted.* ed with his subject, he has it in his power to exhibit a great variety of very striking experiments which can never fail to arrest the attention of the juvenile mind, and prepare it for entering on expla- A knowledge of certain departments of the manations of some of the sublimest phenomena of na- thematical sciences is essentially requisite for unture. But without these instruments very few ex- derstanding many of the discussions and investigaperiments of any degree of interest can be performed tions connected with natural philosophy, astronomy, in relation to these subjects. The illustration of the geography, and navigation, and for various practiphenomena of magnetism requires no expensive ap- cal purposes in the mehanical arts; and, conseparatus. Two or three small, and as many large quently, ought to form a portion of every course of bar magnets a large horse-shoe magnet, a mag- general education. During the first stages of elenetic compass, and a few needles, pieces of iron, mentary instruction, a knowledge of the names and and steel filings, may be sufficient for illustrating some of the properties of angles, triangles, squares, the prominent facts in relation to this department parallelograms, trapezoids, trapeziums, circles, of philosophy. But as I have already thrown out a ellipses, parallels, perpendiculars, and other geomcfew hints on this subject in the lesson on the Saga-trical lines and figures, may be imparted, on differcious Swan, it would be needless to enlarge. My ent occasions, by way of amusement, as is generally only reason for suggesting the above hints and ex- done in infant schools, which would prepare the periments is, to show that any teacher, at a very way for entering on the regular study of mathemasmall expense, may have it in his power to illus- tical science. The usual method of teaching mathetrate, in a pleasing manner, many of the most inter- matics is to commence with the "Elements of Euesting and practical truths connected with natural clid," proceeding through the first six, and the elephilosophy. Most of the apparatus alluded to venth and twelfth books, and afterwards directing above could be procured for two or three pounds, the attention to the elements of plane and spherical provided the experimenter apply his hands and con- trigonometry, conic sections, fluxions and the highstruct a portion of it himself, which he can easily er algebraic equations, in which the attention of the do when the materials are provided. In regard to student is chiefly directed to the demonstration of philosophical apparatus of every description, were mathematical propositions, without being much exthere a general demand for it from all classes of ercised in practical calculations. This is the scienthe community, it might be afforded for less than tific method of instruction generally pursued in colone half the price now charged for it, as certain leges and academies, and if youths of the age of portions of it might be constructed of cheaper mate- fourteen or fifteen were capable of the attention and rials than are now used; as elegance in such instru- abstraction of angelic beings, it would likewise be ments is not always necessary for use; as competi- the natural method. But a different method, I pretion would reduce their price to the lowest rate, and sume, ought to be pursued in schools chiefly devoted as there would be no necessity for great profits when to popular instruction. After the pupil has acquired the manufacturers were certain of a quick and ex- a competent knowledge of arithmetic, let him be tensive sale. conducted through the different branches of practical geometry, including the mensuration of surfaces and solids, artificers' work and land-surveying, exhibiting occasionally a demonstration of some of the rules, in so far as he is able to comprehend it.— After which, a selection should be made from Euclid, (chiefly from the first book,) of those propositions which have a practical bearing, and which from the foundation of practical geometry and the Chemistry.—Chemistry, in its present improved state, is a science so interesting and useful, so intimately connected with the knowledge of nature, the improvement of the useful arts, and with every branch of physical and practical science, that an outline, at least, of its leading principles and facts should be communicated to all classes of the young. The distinguishing properties of the simple substances, such as oxygen, nitrogen, carbon, hydrogen, chlorine, iodine, sulphur, and phosphorus-particularly oxygen, nitrogen, carbon, and carburetted hydrogen, should be minutely described, and illustrated by experiments, and their extensive influence in the system of nature particularly detailed. The laws of chemical affinity-the nature and properties of heat, its radiation and expansive power, and the effects it produces on all bodies-the composition and decomposition of water, the nature of crystallization, the properties of earths, and metals, acids, and alkalies, the nature of combustion, chemical action and combinations, the component principles of animal and vegetable substances, and various other particulars, may be impressed upon the minds of the young, and rendered familiar by a variety of simple experiments which can be easily performed. Many of the most important and luminous facts of this science may be exhibited by the aid of a few Florence flasks, glass tubes, common phials, tumblers, wine and ale glasses of which I intended exhibiting some specimens, had my limits permitted. In the meantime I refer the reader to Accum's volume entitled "Chemical Amusements," which contains a perspicuous description of nearly 200 interesting experiments on this subject, with an expla *Notwithstanding the numerous excellent treatises on natural philosophy and chemistry which have been published of late years, we have scarcely any books on these subjects exactly adapted for the use of schools. Blair's "Grammar of Natural Philosophy," and " Conversations" on the same subject by Mrs. Marcet, contain a comprehensive view of the leading subjects of natural philosophy, which may be recommended to the perusal of young persons; but they are scarcely adapted to the purpose of teaching. Dr. Comstock of America, formerly mentioned, (page 75,) lately published a "System of Natural philosophy," for the use of students and preceptors, which has already passed through nine editions. This volume contains about 300 closely printed pages, and above 200 wood-cuts, and comprises a popular and scientific illustration of the "Properties of Bodies, Mechanics, Hydrostatics, Hydraulics, Pneumatics, Acoustics, Optics, Astronomy, Electricity, and Magnetism," with questions in the margin of every page for exercising the judgment of the student. It is calculated for being an excellent text-book in colleges and academies; but would require to be somewhat reduced and simplified, to adapt it to the use of common schools. |