[From Katun, Vol. xi.] 



LXXI. On the Dynamical Evidence of the Molecular Constitution of Bodies*. 



WHEN any phenomenon can be described as an example of some general 

 principle which is applicable to other phenomena, that phenomenon is said to be 

 explained. Explanations, however, are of very various orders, according to the 

 degree of generality of the principle which is made use of. Thus the person 

 who first observed the effect of throwing water into a fire would feel a certain 

 amount of mental satisfaction when he found that the results were always 

 similar, and that they did not depend on any temporary and capricious anti- 

 pathy between the water and the fire. This is an explanation of the lowest 

 order, in which the class to which the phenomenon is referred consists of other 

 phenomena which can only be distinguished from it by the place and time of 

 their occurrence, and the principle involved is the very general one that place 

 and time are not among the conditions which determine natural processes. On 

 the other hand, when a physical phenomenon can be completely described as a 

 change in the configuration and motion of a material system, the dynamical 

 explanation of that phenomenon is said to be complete. We cannot conceive 

 any further explanation to be either necessary, desirable, or possible, for as soon 

 as we know what is meant by the words configuration, motion, mass, and force, 

 we see that the ideas which they represent are so elementary that they cannot 

 be explained by means of anything else. 



The phenomena studied by chemists are, for the most part, such as have 

 not received a complete dynamical explanation. 



Many diagrams and models of compound molecules have been constructed. 

 These are the records of the efforts of chemists to imagine configurations of 

 material systems by the geometrical relations of which chemical phenomena may 



A lecture delivered at the Chemical Society, Feb. 18, by Prof. Clerk-Maxwell, F.R.S. 



