14 Mr. J. Croll on What determines Molecular Motion P — 



Here we have the energy assuming in succession five or six differ- 

 ent forms. While the particles are combining we call the 

 energy chemical ; when the electric current is produced we de- 

 signate the energy electrical: when magnetism is produced we 

 designate it magnetic ; and when the machine is in motion we 

 call it mechanical, and so forth. It is the same energy under 

 all these various forms. The only difference . between che- 

 mical, electric, magnetic, and heat energy is merely in the 

 mode of operation. The difference lies therefore not in the 

 force or energy itself, but in its determinations. If we regard 

 heat, light, electricity, magnetism, chemical action, &c. as but 

 different modes of motion, as they in reality probably are, then 

 the difference between chemical action and heat, or between heat 

 and electricity, or between electricity and magnetism, or between 

 magnetism and mechanical motion, &c., depends wholly on the 

 cause of the determination of motion. The difference does not lie 

 in the mere exertion of force, but in the waij or manner in which 

 force is exerted. 



We may now consider the bearing which these propositions 

 relating to the determination of motion have on some of the 

 questions which at the present time are agitating scientific minds. 



Let us consider, first, their bearing on theories regarding "vital 

 force '' and the mystery of life. 



Theories of Life. 



To a large extent the discussions and diversity of opinion 

 which at present prevail in reference to the mystery of life and 

 the distinction between the organic and the inorganic world take 

 their rise from confusion of ideas regarding the difference be- 

 tween the cause of motion and the cause of the determination of 

 motion. The various theories maybe divided into two classes, — 

 the advocates of the one class maintaining that all the pheno- 

 mena of life, all the changes which take place in organic nature 

 are the result of purely chemical and physical agencies ; while the 

 other party maintain that there must be something more than 

 the ordinary chemical and physical forces at work — in short, that 

 life and organic nature imply the action of a force altogether 

 different from those which belong to the domain of chemistry 

 and physics, and to which the name of '' Vital Force " has been 

 apphed. 



Both parties appear to be to a certain extent right, and both to 

 a certain extent wrong. Let us begin with the consideration of 

 the Vital-Force theory. 



In what respect, then} is vital force supposed to differ from 

 other forces ? Does the difference exist in the force itself, or in 

 the mode of its operation ? Is vital force the same as the che- 



