BOOK II.'* RELATIVE INCREASE OF MOTION. 635 



tlie flame of fire-arms is seen sooner tlian the sound is heard, 

 jilthougli tlie ball must have struck the air before the flame, 

 which was behind it, eoukl escape : the reason of which is, that 

 hght moves with greater velocity than sound. We perceive, 

 also, that visible images are received by the sight with greater 

 rapidity than they are dismissed, and for this reason, a violin 

 string touched with the finger appears double ov triple, because 

 the new image is received before the former ouo is dismissed. 

 Hence, also, rings when spinning appear globuka-p and a lighted 

 torch, borne rapidly along at night, appears to havo a tail. Upon 

 the principle of the inequality of motion, also, Galileo attempted 

 an explanation of the flood and ebb of the sea, supposing the 

 earth to move rapidly, and the water slowly, by which means the 

 ■water, after accumuhiting, would at intervals fall back, as is 

 shown in a vessel ot" water made to move rapidly. He has, how- 

 ever, imagined this on data which cannot be granted (namely, 

 the earth's motion), and besides, does not satis lactorily account 

 for the tide taking place every six hours. 



An example of our present point (the relative measure of 

 motion), and, at the same time, of its remarkable use of which 

 we have spoken, is conspicuous in mines filled with gunpowder, 

 where immense weights of earth, buildings, and the like, are 

 overthrown and prostrated by a small quantity of powder ; the 

 reason of which is decidedly this, that the motion of the expan- 

 sion of the gunpowder is much more rapid than that of gravity,"* 

 which would resist it, so that the former has terminated before 

 the latter has commenced. Hence, also, in missiles, a strong blow 

 will not carry them so far as a sharp and rapid one. Nor could 

 a small portion of animal spirit in animals, especially in such 

 vast bodies as those of the whale and elephant, have ever bent or 

 directed such a mass of body, were it not owing to the velocity of 

 the former, and the slowness of the latter in resisting its motion. 



In short, this point is one of the principal foundations of the 

 magic experiments (of which we shall presently speak), where a 

 small mass of matter overcomes and regulates a much larger, if 

 there but be an anticipation of motion, by the velocity of one 

 before the other is prepared to act. 



Finally, the point of the first and last should be observed 

 ia all natural actions. Thus, in an infusion of rhubarb the pur- 

 gative property is first extracted, and then the astringent ; we 

 liave experienced something of the same kind in steeping violets 

 in vinegar, which first extracts the sweet and delicate odour of 



^ The author in the text confounds inertness, which is a simpld 

 indifference of bodies to action, with gravity, which is a force acting 

 always in proportion to their density. He falls into the same error 

 turther on. Ed. 



