We may judge of the very imperfect state in which the theory of mechanics was at that time, by the astonishment expressed by King, Iliero, when Archimedes exclaimed, " Give me a place to stand on, and I will move the earth !" a pro position which could have excited no surprise in any person possessing a knowledge of the simple property of the lever. Of the theory of motion, however, it does not appear that even Archimedes possessed any adequate idea ; the proper ties of' uniform motion seem only to have engaged the attention of the ancients, and with those of accelerated and variable motion they were totally unacquainted: these were subjects to which their geometry could not be applied, the modern analysis being necessary to bring this branch of the science to perfection.
From the time of Archimedes till the commencement of the sixteenth century, the theory of' mechanics appears to have remained in the same state in which it was left by this prince of Grecian science, little or no additions having been made to it during so many ages; lint about this time, Stevinus. a Flemish mathematician, made known directly, without the introduction of the lever, the laws of equilibrium of a body placed on an inclined plane : he also investigated with the saute success. many other questions on statics, and d-termined the conditions of equilibrium between several forces concurring in a common point, which collies, in fact, to the celebrated relating to the parallelogram of forces; but it does not appear that he was at all aware of its consequences and application. In 1593, Galileo composed a
treatise on statics, which he reduced to this single principle, viz :—It requires an equal power to raise two (Efferent bodies to heights having the inverse ratio of their weights: that is, whatever power will raise a body of two pounds to the height of one foot, will raise a body of one pound to the height of two feet. On this simple principle he investigated the theory of the inclined plane, the screw, and all the mechanical powers : and Descartes afterwards employed it in consider ing the statical equilibriums of machines in general, but with out quoting Galileo, to whom he had been indebted or the first idea. After Stevinus and Galileo, Torricelli, Descartes, Huygens, Wallis, Wren, Newton, Liebnitz, Dechales, Oughtred, Kcil, Delahire, Lagrange, Atwood, Irony, Emer son, Watt, Gregory, Young, &c., have in succession, since the period to which we have alluded, explained and applied the principles of this civilizing science in a wonderful manner.