BOOK II.] INSTANCES OF QUANTITY. 55? 



XLVII. In tlie twenty-third rank of prerogative instances we 

 will place instances of quantity, which we are also wont to call 

 the doses or&quot; nature (borrowing a word from medicine). They 

 are sucli as measure the powers by the quantity of bodies, and 

 point out the effect of the quantity in the degree of power. And 

 m the first place, some powers only subsist in the universal 

 quantity, or such as beats a relation to the confirmation and 

 fabric of the universe. Thus the earth is fixed, its parts fall. 

 The waters in the sea flow and ebb, but not in the rivers, except 

 by the admission of the sea. Then, again, almost all particular 

 powers act according to the greater or less quantity of the body. 

 Large masses of water are not easily rendered foul, small are. 

 New wine and beer become ripe and drinkable in small skins 

 much more readily than in large casks. If an herb be placed in 

 a considerable quantity of liquid, infusion takes place rather than 

 impregnation ; if in less, the reverse. A bath, therefore, and a 

 light sprinkling, produce different effects on the human body. 

 Light dew, again, never falls, but is dissipated and incorporated 

 with the air ; thus we see that in breathing on gems, the slight 

 quantity of moisture, like a small cloud in the air, is immediately 

 dissolved. Again, a piece of the same magnet does not attract 

 BO much iron as the whole magnet did. There are some powers 

 where the smallness of the quantity is of more avail ; as in 

 boring, a sharp point pierces more readily than a blunt one ; the 

 diamond, when pointed, makes an impression on glass, and the 

 like. 



Here, too, we must not rest contented with a vague result, but 

 inquire into the exact proportion of quantity requisite for a par 

 ticular exertion of power; for one would be apt to suppose that 

 the power bears an exact proportion to the quantity ; that if a 

 leaden bullet of one ounce, for instance, would fall in a ^iven 

 time, one of two ounces ought to fall twice as rapidly, which is 

 most erroneous. Nor does the same ratio prevail in every kind 

 of power, their difference being considerable. The measure, 



mena are discovered to afford a general rule which will apply to any 

 concrete case, the deductive method must be applied, and the elemen 

 tary principles made through its agency to account for the laws oi their 

 more complex combinations. The reflection and retraction ot light by 

 the rain falling from a cloud opposite to the sun was thought, even 

 before Newton s day, to contain the form ot the rainbow. This philo 

 sopher transformed a probable conjecture into a certain fact when ho 

 deduced from the known laws ot reflection and retraction the breadth 

 of the coloured arch, the diameter of the circle of which it is a part, 

 and the relation of the latter to the place ol the spectator and the sun. 

 Doubt was at once silenced when there came out ol his calculus a com 

 bination of the same laws ot the simple elements of optics answering tfl 

 the phenomena in nature. Ed. 



