OF NATURAL PHILOSOPHY. 297 



giving to them properties differing extremely from 

 each other. 



(333.) The inherent activity of matter is proved 

 not only by the production of motion by the mutual 

 attractions and repulsions of distant or contiguous 

 masses, but by the changes and apparent trans- 

 formations which different substances undergo in 

 their sensible qualities by mere mixture. If water 

 be added to water, or salt to salt, the effect is an 

 increase of quantity, but no change of quality. In this 

 case, the mutual action of the particles is entirely me- 

 chanical. Again, if a blue powder and a yellow one, 

 each perfectly dry, be mixedandwell shaken together, 

 a green powder will be produced ; but this is a mere 

 effect arising in the eye from the intimate mixture 

 of the yellow and blue light separately and inde- 

 pendently reflected from the minute particles of 

 each ; and the proof is had by examining the mix- 

 ture with a microscope, when the yellow and blue 

 grains will be seen separate and each quite unaltered. 

 If the same experiment be tried with coloured 

 liquids, which are susceptible of mixing without 

 chemical action, a compound colour is likewise pro- 

 duced, but no examination with magnifiers is in that 

 case sufficient to detect the ingredients ; the reason 

 obviously being, the excessive minuteness of the 

 parts, and their perfect intermixture, produced by 

 agitating two liquids together. From the mixture 

 of two powders, extreme patience would enable any 

 one, by picking out with a magnifier grain after grain, 

 to separate the ingredients. But when liquids are 

 mixed, no mechanical separation is any longer prac- 

 ticable ; the particles are so minute as to elude all 



