39 6* THE POPULAR SCIENCE MONTHLY. 



energy and structure, are closely connected : to determine the exact 

 relations existing between these, under stated conditions, is still the 

 fundamental problem of chemical science. 



We can define energy : the phlogisteans could not define phlo- 

 giston. But in the ethereal philosophy of the future will it not be said 

 of the present workers in science that they could not define ether, but 

 even spoke of it at times as " not gross nor ponderable matter " ? The 

 theory of phlogiston was continued and developed in the theory of 

 caloric : the theory of caloric is vastly extended, simplified, and ren- 

 dered definite in the theory of energy, and the theory of energy seems 

 destined to be largely extended by the ethereal theory now in its infancy. 



Mankind has until lately been content with space of three dimen- 

 sions, but the bolder and more dashing spirits among the mathema- 

 ticians have dared to look forward to a better world than this where 

 they may revel in space of four dimensions. What a strange world 

 must that be ! what a fearful place for a mathematical examination, 

 when we remember that the inhabitants thereof if there be inhabi- 

 tants may turn spherical hollow balls inside out without tearing or 

 breaking them ! 



While we look forward to the future of science with hope, I think 

 we ought not to look back on the former workers without respect. 



But I must pass on to consider the second of the great theories 

 which have paved the way for the doctrines of modern chemistry. 

 The germ of the modern ideas of substitution, valency, atom-linking, 

 etc., is, I believe, to be found in the pure dualism of Berzelius ; and, 

 moreover, the influence of the dualistic ideas of that great chemist seems 

 to me easily traceable in the essentially unitary system of modern chem- 

 istry. The chemistry of Lavoisier centered around the wonderful sub- 

 stance whose properties he so carefully studied. The teaching of the 

 great founder of modern chemistry was saturated with ideas suggested 

 by the study of oxygen. The compounds of oxygen were divided by 

 Lavoisier into two groups, bases and acids : when these reacted chem- 

 ically, a salt that is, a body made up of base and acid was produced. 

 Berzelius developed these ideas until he had constructed a complete 

 and beautiful theory, viewed in the light of which all compounds were 

 of analogous structure. Every chemical substance was made up, ac- 

 cording to the Swedish chemist, of two parts ; these parts might them- 

 selves be composed of simpler parts, or they might be truly element- 

 ary. The two parts of a compound were respectively endowed with 

 .positive and negative electricity. When two bodies combined, the 

 positive electricity in one neutralized the negative electricity in the 

 other ; hence the phenomena of light and heat noticed in chemical 

 combination. An element might contain an absolutely greater quan- 

 tity of positive electricity than another and nevertheless belong to the 

 electro-negative series of elements : thus sulphur and oxygen readily 

 combine to form a substance which, when dissolved in water, yields an 



