sity of their action, or the acceleration they produce in a given time, is the same, whether the body acted upon be at rest or in motion; in others it is greatest when the body acted on is at rest, and becomes less as its velocity increases. Gravity is the only force which is certainly known to act with equal intensity on bodies in motion, and at rest; though magnetism probably possesses the same property. Every other important power acts more forcibly on a body at rest, than on one which has already acquired motion in the direction in which it acts.* This happens with the strength of animals, the impulse of fluids, and the elasticity of springs. ANIMAL POWER. 'Muscular energy is exerted through the contraction of the fibres which constitute animal muscles. The bones act as levers to facilitate and direct the application of this force, the muscles operating on them through the medium of tendons, or otherwise. Muscular power is much greater in some animals, than it is in man, owing to their size, or more active mode of life. It is greatest in beasts of prey. 'Men.-The power of a man to produce motion in weights or obstacles, varies according to the mode in which he applies his force, and the number of muscles which are brought into action. In the operation of turning a crank, a man's power changes in every part of the circle which the handle describes. It is greatest when he pulls the handle upward from the height of his knees, next greatest when he pushes it down on the opposite side, though here the power cannot exceed the weight of his body, and is therefore less than can be exerted in pulling upward. The weakest points are at the top and bottom of the circle, where the handle is pushed or drawn horizontally. 'If a windlass be provided with two cranks placed at right angles with each other, two men will perform much more work, than they could if the cranks were disconnected, because at the moment one puts forth his strength to the least advantage, the other is exerting his with the greatest effect. 'The mode in which a man can exert the greatest active strength, is in pulling upward from his feet, because the strong muscles of the back as well as those of the upper and lower extremities, are then brought advantageously into action, and the bones are favorably situated by the fulcra of the levers being near to the resistance. Hence the action of rowing is one of the most advantageous modes of muscular exertion, and no method which has been devised for propelling boats by the labor of men, has hitherto superseded it. 'According to Mr Buchanan, the comparative effect produced by different modes of applying the force of a man, is nearly as * See Playfair's Outlines of Natural Philosophy, vol. i. p. 107. follows. In the action of turning a crank, his force may be represented by the number 17. In working at a pump, by 29. In pulling downward, as in the action of ringing a bell, by 39. And in pulling upward from the feet, as in rowing, by 41.* 'In estimating the different applications of animal force, we must take into consideration not only the resistance they can overcome, but the velocity with which they move, and the length of time for which they can be continued. Violent efforts are not true specimens of a man's labor, since they can be exerted for a short time only. A moderate computation of an ordinary man's uniform strength, is, that he can raise a weight of 10 pounds to the height of 10 feet once in a second, and continue this labor for ten hours in the day. This is supposing him to use his force under common mechanical advantages, and without any reduction for friction. 'Horses.-Horses are often employed as movers of machinery by their draught. A horse draws with greatest advantage when the line of draught is not horizontal, but inclines upward, making a small angle with the horizontal plane, as already stated, page 197. The force of a horse diminishes as his speed increases. The following proportions are given by Professor Leslie for the force of the horse employed under different velocities. If his force when moving at the rate of two miles per hour, is represented by the number 100, his force at three miles per hour will be 81,-at four miles per hour 64,-at five miles 49,-and at six miles 36. These results are confirmed very nearly by the observations of Mr Wood. In this way the force of a horse continues to diminish, till he attains his greatest speed, when he can barely carry his own weight. 'Various estimates have been made of a horse's power, by Desaguliers, Smeaton, and others, but the estimate now generally adopted as a standard for measuring the power of steam engines, is that of Mr Watt, whose computation is about the average of those given by the other writers. The measure of a horse's power, according to Mr Watt, is, that he can raise a weight of 33000 pounds to the height of one foot in a minute. In comparing the strength of horses with that of men, Desaguliers and Smeaton consider the force of one horse to be equal to that of five men; but writers differ on this subject. 'When a horse draws in a mill or engine of any kind, he is commonly made to move in a circle, drawing after him the end of a lever which projects like a radius from a vertical shaft. Care should be taken that the horse-walk, or circle, in which * See Brewster's Edition of Ferguson's Mechanics, vol. ii. p. 9. The whole numbers are 1742, 2856, 3883, and 4095. Young's Lectures on Natural Philosophy, vol. i. p. 101. he moves, be large enough in diameter, for since the horse is continually obliged to move in an oblique direction, and to advance sideways as well as forward, his labor becomes more fatiguing, in proportion as the circle in which he moves becomes smaller. 'In some ferry boats and machines, horses are placed on a revolving platform, which passes backward under the feet whenever the horse exerts his strength in drawing against a fixed resistance, so that the horse propels the machinery without moving from his place. A horse may act within still narrower limits, if he is made to stand on the circumference of a large vertical wheel, or upon a bridge supported by endless chains which pass round two drums, and are otherwise supported by friction wheels. Various other methods have been practised for applying the force of animals, but most of them are attended with great loss of power, either from friction, or from the unfavorable position of the animal.'-pp. 253--257. Chapter XIII. treats of the Arts of Conveying Water; XIV. Arts of Dividing and Uniting Solid Bodies; XV. Arts of Combining Flexible Fibres; XVI. Arts of Horology; XVII. Arts of Metallurgy; XVIII. Arts of Communicating and Modifying Colors; XIX. Arts of Vitrification; XX. Arts of Induration by Heat; the XXI., and last chapter is on the Preservation of Organic Substances, ART. IV. Remarks on the Duty of States in regard to Public Education. A SYSTEM of education which may give to every member of American society, a portion of knowledge adequate to the discharge of his duties as a man and a citizen of the republic, is essential to the advancement of private interest, the maintenance of public virtue, the due appreciation of talents, the preservation of a sacred regard to principle, and of a high tone of moral sentiment. A system which affords to such as are endowed with superior capacities, the means of making proportional attainments, is also intimately connected with the interest of the nation at home, through those who administer, and abroad through those who represent our government; with the extension of just and liberal opinions in relation to the effect of free governments; with the union and fraternity subsisting between the members of the confederacy, and with the general character of the nation for liberal sentiments and grateful recollections. If these statements be just, we are led to ask under what authority the blessings of learning are to be secured to the nation? The government of the Union has manifested no decided inclination to act efficiently in the matter. And as the legislative department has shown no disposition to exercise its acknowledged powers, in relation to this subject, even within the district where it possesses sole dominion, it is not to be expected that the same power should be extended over the whole nation, where a plausible, at least, if not valid Constitutional objection may be raised against its exercise ;-and much less are we to suppose that the concerns of education will supersede, in the minds of executive officers, the great subjects of war and peace, of commerce and revenue, of foreign embassies and international relations. These great, absorbing interests will of necessity continue to engross the attention and speculations of the active, aspiring candidates for public distinctions and emoluments. Happy will it be for the community, if those whom it delights to honour with a station in this department, shall themselves be at all times found experimentally acquainted with the advantages of a sound and finished education, united with commanding talents, and an integrity above suspicion. A statesman with these qualifications cannot fail to exercise an important indirect, if not immediate influence on the standard of taste, knowledge, and refinement throughout the land, and to stimulate by countenance and example what he may not be able to support by positive legal provisions. In proportion, however, as knowledge, whether elementary or profound, is to be regarded as a blessing, in the same degree is the want of it, to be esteemed a misfortune. Each and every portion of this Union has therefore an interest in the success of every effort to diffuse the means of education, separate from any calculation of profit and loss, and from any reference to the great and momentous national concern, already mentioned as involved in this subject. Indeed there are various interests besides that of ededucation, in which the nation at large has a deep stake; yet the general legislature cannot, consistently with its prescribed powers, materially interfere. Such are the encouragement of agriculture, the bestowing of charters for local establishments, whose effects, notwithstanding, are felt far beyond the sphere of their immediate operation. Adverting to the manner in which these interests are, and must continue to be managed among us, we are furnished with an answer to our inquiry by what authority the benefits of learning are to be conferred on the whole American community. The separate State legislatures, have in several instances already practically settled the question, by a long course of legislation on the subject. Others have contented themselves with partial, inconsiderable efforts applied to a class of persons not the most likely to appreciate the blessings of knowledge, and least disposed to acknowledge an obligation which places them in a degraded relation to their fellow citizens. A third class of States are still wavering between a resolution to provide an efficient system of education for themselves, and a vague, perhaps a vain, hope, that something may still be expected from the liberality or the justice of the general government, towards this object. We cannot refrain from expressing in this place the admiration excited by the policy of one enlightened State, which, while engaged in an enterprise for internal improvement, the grandest that our country has ever witnessed, perhaps that the genius of man has ever devised, simultaneously erected a system of universal as well as liberal education, by means of which more than eight thousand ordinary, and numerous superior seminaries are put into operation, and more than 400,000 youths of both sexes are annually admitted to the inestimable blessings of either solid or useful, or polite and finished education. To estimate justly the immense influence of that amount of talent which will thus be brought from a dormant to an active condition, is perhaps beyond the power of calculation. To behold its full display, we must search every cottage and farm house as well as every mansion, for the energy and enterprise, united with the firmness and sobriety of character which it has developed; we must note the change from a devotion to material life and animal gratifications, to a pursuit of intellectual speculations; we must penetrate, in short, every bosom made in any degree capable of being warmed by the radiance of genius, or filled with loftier and purer sentiments. An apprehension has sometimes been indulged, that the interests of the several States would become merged and lost in that of the confederation. Nothing is better fitted to preserve the distinct individuality of the States, than reserving to themselves the superintendence of the concerns of education. Not |