is incident, and to produce a chemical effect on the constitution of his patient, if he is ignorant either of the processes which are going on in the system, of the chemical properties of the substances which he throws into it, or of the effects which they will certainly produce? If he is ignorant of the chemical affinities that subsist between the various articles of the Materia Medica, he may often administer preparations which are not only inefficacious, but even poisonous and destructive to his patient. When two chemical substances, each of which might be administered separately with safety, are combined, they sometimes produce a substance which is highly deleterious to the animal system. For example, although mercury and oxygenized muriatic acid have both been administered, and either of them may be taken separately without injury to the animal economy, yet if a medical practitioner, ignorant of the chemical affinities of such substances, and of the quality of the compound, should give both of them in conjunction, the most dreadful consequences might ensue ; since the product of this mixture, oxygenized muriate of mercury, is known to be a most corrosive poiand there can be little doubt that hundreds of lives have been destroyed, by ignorant pretenders to medical science, in consequence of the injudicious administration of such deleterious preparations.

son;

But chemistry is not the only science which is of utility in the arts which minister to the comfort and pecuniary interests of society. Geometry, trigonometry, conic sections, and other branches of mathematical knowledge; hydrostatics, hydraulics, mechanics, optics, botany, mineralogy and the other departments of the physical sciences, may be rendered of essential service to artisans and mechanics of vari

ous descriptions. All the sciences are, in some degree, connected, and reflect a mutual light upon one another; and consequently the man who has the most extensive acquaintance with science, is best qualified for carrying to perfection any one department of the useful arts.

Practical Geometry is highly useful to almost every mechanic and artisan, particularly to millwrights, bricklayers, carpenters and masons. It teaches them to form angles of any assigned number of degrees, to draw parallel and perpendicular lines, to proportion circumferences to diameters, to divide circular rims into any number of parts, to estimate the square or cubical contents of any piece of workmanship, and to calculate the price they ought to receive for any work they perform, according to its solid or superficial dimensions. In forming estimates of the expense of any proposed undertaking, the carpenter, bricklayer, and architect must find such knowledge essentially requisite; and even the common labourer who undertakes the formation of roads, the digging of pits, and the clearing away of rubbish, will find the principles of arithmetic and geometry of important service in estimating the rate at which he can perform such operations. The following geometrical theorems, besides many others, are capable of a variety of practical applications, in many departments of the arts. "If, from the two ends of any diameter of the circle, two lines be drawn to meet in any one point of the circle whatever, such lines are perpendicular to each other," or, in other words, they form a right angle at the point of contact.* Again, "The areas of all circles are in exact proportion to

* For example, if from the two ends of the diameter A and

the squares of their radii, or half diameters." If, for example, we draw a circle with a pair of compasses whose points are stretched 4 inches asunder, and another with an extent of 8 inches, the large circle is exactly four times the size or area of the small one. For the square of 4 is=16, and the square of 8 is= 64, which is four times 16. And as the circumferences of the circles are in proportion to the radii, it will follow, that the length of a string which would

B

E

C

D

A

B, the lines A C, B C be drawn to the point C, these lines will be perpendicular to each other, and consequently the an gle at C will be a right angle. In like manner the lines A D, and B D, A B and B E, will stand at right angles to each other; and the same will be the case to whatever point of the circle such lines are drawn. The practical application of this principle, in various operations, will, at once, be obvious to the intelligent mechanic, especially when he intends the two ends or sides of any piece of machinery to stand perpendicular to each other.

go round the curve of the larger circle is exactly double the length of one which would go round the lesser. Mechanics, in recognising such theorems, will meet with many opportunities of reducing them to practice. Again, there is a figure which Geometricians term a parabola, which is formed every time we pour water forcibly from the mouth of a tea-kettle, or throw a stone forward from the hand. One property of the parabola is, that if a spout of water be directed at half a perpendicular from the ground, or at an angle of elevation of 45 degrees, it will come to the ground at a greater distance than if any other direction had been given it, a slight allowance being made for the resistance of the air. Hence the man who guides the pipe of a fire-engine may be directed how to throw the water to the greatest distance, and he who aims at a mark, to give the projectile its proper direction. To surveyors, navigators, land-measurers, gaugers and engineers a knowledge of the mathematical sciences is so indispensably requisite, that, without it, such arts cannot be skilfully exercised.

The Physical sciences are also of the greatest utility in almost every department of art. To masons, architects, ship-builders, carpenters and every other class employed in combining materials, raising weights, quarrying stones, building piers and bridges, splitting rocks, or pumping water from the bowels of the earth, -a knowledge of the principles of mechanics and dynamics is of the first importance. By means of these sciences the nature of the lever and other mechanical powers may be learned, and their forces estimated the force produced by any particular combination of these powers calculated-and the best mode of applying such forces to accomplish certain effects, ascertained. By a combination of the mecha

nical powers the smallest force may be multiplied to an almost indefinite extent, and with such assistance man has been enabled to rear works and to perform operations which excite astonishment, and which his own physical strength, assisted by all that the lower animals could furnish, would have been altogether inadequate to accomplish. An acquaintance with the experiments which have been made to determine the strength of materials, and the results which have been deduced from them, is of immense importance to every class of mechanics employed in engineering and architectural operations. From such experiments, (which have only been lately attended to on scientific principles) many useful deductions might be made respecting the best form of mortises, joints, beams, tenons, scarphs, &c. ; the art of mast-making, and the manner of disposing and combining the strength of different substances in naval architecture, and in the rearing of our buildings. For example, -from the experiments now alluded to it has been deduced, that the strength of any piece of material depends chiefly on its depth, or on that dimension which is in the direction of its strain. timber of one inch in breadth, and two inches in depth is four times as strong as a bar of only one inch deep; and it is twice as strong as a bar two inches broad and one deep, that is, a joint or lever is always strongest when laid on its edge. Hence it follows, that the strongest joist that can be cut out of a round tree is not the one which has the greatest quantity of timber in it, but such that the product of its breadth by the square of its depth shall be the greatest possible.-Again, from the same experiments it is found, that a hollow tube is stronger than a solid rod containing the same quantity of matter. This

A bar of