36i8 PHILOSOPHICAL TRANSACTIONS. [ANNOl/yS. 



XVll. Reflections on the Communication of Motion hy Impact and Gravitii. By 

 the Rev. I, Milner, M.A., Fellow of Queens College, Cambridge * p. 344. 



The theory of moving bodies was little understood by the philosophers who 

 lived in the l6th century. They observed, that a body, once put into motion, 

 continued to move for some time after the force was impressed; but they argued 

 very strangely from this ordinary phenomenon, p'ar from considering the air as 

 a resisting medium ; they supposed, with Aristotle, and the ancients, that it was 

 the perpetual influx of the parts of the atmosphere which continued to urge the 

 body forward and preserve its motion. When a body is projected in any direc- 

 tion inclined to the horizon, the gravity of its parts is always observed to bend 

 the direction of its motion into a curve line; and because this gravity remains 

 invariably the same, whatever the force of projection be, in very swift motions, 

 the figure described may approach very nearly to a i-ight line. This last circum- 

 stance induced some of those philosophers to believe, that a cannon ball, for 

 instance, always moves in the same straight line till its velocity is entirely 

 destroyed; and that afterwards it descends towards the earth in a direction 

 perpendicular to the horizon. Others thought they mended the matter by sus- 

 pending the action of gravity for a certain period only; by allowing the latter 

 part of the path to be curvilinear; and lastly, the body to descend to the earth 

 in a straight line, as in the former case. But we, who have now seen the 

 gradual improvements in mechanics from time to time, are not surprized, that 

 men, in the infancy of that science, should have embraced absurd and ridicu- 

 lous principles: we rather wonder, how Tartalea, the author of the notion just 

 mentioned, was able to form any just estimate of the horizontal ranges of pro- 

 jectiles, and to discover their maxima. Whether, by conjecture, or probability 

 of induction, we are unable to determine; but so it was, Tartalea affirmed, 

 what has since been found true on unexceptionable evidence, that the ampli- 

 tudes of projectiles on the horizon, are always greatest when the angles of pro- 

 jection are equal to 45°. But the praise of this discovery, as well as whatever 

 else relates to the accelerated motions of bodies near the surflice of the earth, is 

 justly due to the incomparable Galileo. The theory of mechanics had received 

 no inconsiderable improvement since the time of Archimedes, when this sur- 

 prizing genius appeared in the former part of the 17th century. He discarded 

 the peripatetic philosophy; explained the whole doctrine of accelerated motion 

 and of projectiles: in short, he so much exhausted the subject, that the best 

 treatises we have at this day are little more than a repetition o( Galileo's 

 discoveries. 



This philosopher never attempted to investigate the laws by which motion is 



* Now riiasUr i>( Queen's College. 



