BOOK THE FIEST. 



CHAPTER 1. 



FORCES AND ORGANS. 



Of forces in the inorganic kingdom and among organised beings — Matter 

 reveals itself by its properties — When matter acts, we conclude that 

 forces exist — Multiplicity of forces formerly admitted ; tendency to 

 their reduction to one force in the inorganic kingdom — Indestruc- 

 tibility of force ; its transformations — Yital forces, their multiplicity 

 according to the ancient physiologists — Several vital forces are 

 reduced to physical forces — Of laws in physics and in physiology — 

 General theory of physical forces. 



We know matter only by its 'properties, which we could not 

 conceive of apart from matter. The word property does not 

 answer to anything real : it is an artifice of language ; thus, the 

 expressions, weight, heat, hardness, colour, &c., attributed to 

 various bodies in nature, mean that these bodies manifest 

 themselves to our senses by certain effects which have been 

 made known to us by daily experience. 



When matter acts, that is to say, w^hen it changes its state, 

 there occurs what we call a phenomenon, and by a new appli- 

 cation of language we call the unknown cause which has 

 produced this phenomenon. Force, A body which falls, a 

 river which flows, a fire which warms us, the lightning which 

 flashes, two bodies which combine, &c., all these correspond to 

 manifestations of forces which we call gravity, mechanical 

 force, heat, electricity, light, chemical aflinities, &c. 



In the first ages of science the number of forces was almost 

 infinitely multiplied. Each particular phenomenon was re- 

 garded as the manifestation of a special force. But by degrees 

 it was recognised that divers manifestations might result from 



