418 THE CANADIAN NATURALIST. [Dec. 



only a manifestation of the latter. Denying the existence of a 

 special vital force as such, they retain the term only to express the 

 sum of the phenomena of living beings. 



In calling your attention this evening to the Correlation of the 

 Physical and the Vital Forces, I have a- two-fold object in view. 

 On the one hand, I would seek to interest you in a comparatively 

 recent discovery of Science, and one which is destined to play a 

 most important part in promoting man's welfare; and on the other 

 I would inquire what part our own country has had in these dis- 

 coveries. 



In the first place, then, let us consider what the evidences are 

 that vital and physical forces are correlated. Let us inquire how 

 far inorganic aad organic forces may be considered mutually 

 convertible, and hence, in so far, mutually identical. Thig may 

 best be done by considering, j&rst, what is to be understood by 

 correlation: and second, how far are the physical forces themselves 

 correlated to each other. 



At the outset of our discussion, we are met by an unfortunate 

 ambiguity of language. The word Force, as commonly used, has 

 three distinct meanings; in the first place, it is used to express the 

 cause of motion, as when we speak of the force of gunpowder ; it 

 is also used to indicate motion itself, as when we refer to the force 

 of a moving cannon-ball; and lastly it is employed to express the 

 effect of motion, as when we speak of the blow which the moving 

 body gives.* Because of this confusion, it has been found con- 

 venient to adopt Kankine's snggestion,^ and to substitute the word 

 ' energy' therefor. And precisely as all force upon the earth's 

 surface — using the term force in its widest sense — ma)' be divided 

 into attraction and motion, so all energy is divided into potential 

 and actual energy, synonymous with those terms. It is the 

 chemical attraction of the atoms, or their potential energy, which 

 makes gunpowder so powerful ; it is the attraction or potential 

 energy of gravitation which gives the power to a raised weight. 

 If now, the impediments be removed, the power just now latent 

 becomes active, attraction is converted into motion, potential into 

 actual energy, and the desired effect is accomplished. The energy 

 of gunpowder or of a raised weight is potential, is capable of 

 acting ; that of exploding gunpowder or of a falling weight is 

 actual energy or motion. By applying a match to the gunpowder, 

 by cutting the string which sustains the weight, we convert 

 potential into actual energy. By potential energy, therefore, is 



