42 THE PEOGKESS AND SPIEIT OF 



actions, may be reduced to a common principle with what 

 we term mechanical forces. And if gravitation be ever 

 submitted to* some common law with other powers, such 

 law will probably be founded on the nature and functions 

 of these ultimate particles, the acofjuara aBiaipsra of 

 ancient philosophy, the materials on which modern science 

 works, amidst the most profound mysteries of the natural 

 world. 



The whole science and exquisite art of photography, in the 

 relations it establishes between light and molecular changes, 

 gives further evidence that these changes form what may 

 justly be deemed the substratum of all physical know- 

 ledge. And the same inference is derived from the discovery 

 of what have been called allotropic states of various sub- 

 stances, as phosphorus, oxygen, &c. ; where an entire change 

 of physical properties is produced, the matter so changed 

 retaining, as far as experiment can tell us, its exact identity 

 of nature. The supposition of an altered arrangement of 

 similar constituent atoms, is the sole present method of 

 explaining this curious phenomenon. 



We name these few instances out of many equally re- 

 markable ; all expounding, in one form or other, the great 

 principle of molecular action and relation, to the clear con- 

 ception of which modern science owes so much of its success. 

 Even the points still open to controversy such as the true 

 nature of the distinction between para-magnetic and dia- 

 magnetic bodies (those which take position parallel to the 

 line of magnetic force, or transversely to it) are clearly 

 seen to depend for solution on more exact knowledge of the 

 modes of molecular aggregation, and their influence on the 

 forces which traverse them. Again, we have the question 

 before noticed, as to the phenomena of the electrical induction 

 through air, glass, and other media ; whether these are due 

 to physical causes yet unknown ? or to molecular polarities 



