THE DYNAMICAL EVIDENCE OF THE MOLECULAR CONSTITUTION OF BODIES. 419 



be illustrated or explained. No chemist, however, professes to see in these 

 diagrams anything more than symbolic representations of the various degrees of 

 closeness with which the different components of the molecule are bound 

 together. 



In astronomy, on the other hand, the configurations and motions of the 

 heavenly bodies are on such a scale that we can ascertain them by direct 

 observation. Newton proved that the observed motions indicate a continual 

 tendency of all bodies to approach each other, and the doctrine of universal 

 gravitation which he established not only explains the observed motions of our 

 system, but enables us to calculate the motions of a system in which the 

 astronomical elements may have any values whatever. 



When we pass from astronomical to electrical science, we can still observe 

 the configuration and motion of electrified bodies, and thence, following the 

 strict Newtonian path, deduce the forces with which they act on each other ; 

 but these forces are found to depend on the distribution of what we call 

 electricity. To form what Gauss called a " construirbar Vorstellung " of the in- 

 visible process of electric action is the great desideratum in this part of science. 



In attempting the extension of dynamical methods to the explanation of 

 chemical phenomena, we have to form an idea of the configuration and motion 

 of a number of material systems, each of which is so small that it cannot be 

 directly observed. We have, in fact, to determine, from the observed external 

 actions of an unseen piece of machinery, its internal construction. 



The method which has been for the most part employed in conducting 

 such inquiries is that of forming an hypothesis, and calculating what would 

 happen if the hypothesis were true. If these results agree with the actual 

 phenomena, the hypothesis is said to be verified, so long, at least, as some one 

 else does not invent another hypothesis which agrees still better with the phe- 

 nomena. 



The reason why so many of our physical theories have been built up by 

 the method of hypothesis is that the speculators have not been provided with 

 methods and terms sufficiently general to express the results of their induction 

 in its early stages. They were thus compelled either to leave their ideas vague 

 and therefore useless, or to present them in a form the details of which could 

 be supplied only by the illegitimate use of the imagination. 



In the meantime the mathematicians, guided by that instinct which teaches 

 them to store up for others the irrepressible secretions of their own minds, 



532 



