438 JAMES CLERK MAXWELL. [CHAP. XIV. 



knowledge, to expound physical optics to persons not pro- 

 fessedly mathematicians. The second reason is, that it is 

 extremely easy to show such persons the phenomena, which 

 are very beautiful in themselves, and this is often accepted 

 as instruction in physical optics. 



4th. The development of the doctrine of the Conservation 

 of Energy. This has produced a far greater effect on the 

 thinking world outside that of technical thermodynamics. 



As the doctrine of the conservation of matter gave a 

 definiteness to statements regarding the immateriality of 

 the soul, so the doctrine of the conservation of energy, when 

 applied to living beings, leads to the conclusion that the 

 soul of an animal is not, like the mainspring of a watch, the 

 motive power of the body, but that its function is rather 

 that of a steersman of a vessel, not to produce, but to regu- 

 late and direct the animal powers. 



5th. The discoveries in Electricity and Magnetism labour 

 under the same disadvantages as those in Light. It is diffi- 

 cult to present the ideas in an adequate manner to laymen, 

 and it is easy to show them wonderful experiments. 



6th. On the other hand, recent developments of Mole- 

 cular Science seem likely to have a powerful effect on the 

 world of thought. The doctrine that visible bodies appar- 

 ently at rest are made up of parts, each of which is moving 

 with the velocity of a cannon ball, and yet never departing 

 to a visible extent from its mean place, is sufficiently startling 

 to attract the attention of an unprofessional man. 



But I think the most important effect of molecular 

 science on our way of thinking will be that it forces on our 

 attention the distinction between two kinds of knowledge, 

 which we may call for convenience the Dynamical and 

 Statistical. 



The statistical method of investigating social questions 

 has Laplace for its most scientific and Buckle for its most 

 popular expounder. Persons are grouped according to some 

 characteristic, and the number of persons forming the group 

 is set down under that characteristic. This is the raw 

 material from which the statist endeavours to deduce general 



