50 MEMORIAL SKETCH. 



To Mrs. Carpenter, of Bristol 



London, 1849. 



I am longing for a little leisure to write out my paper for the 

 Royal Society, on the " Vital and Physical Forces ; " and will 

 rivOw try and give you some idea of it, as well as of some specu- 

 lations which have arisen in my mind in connection with it, and 

 on which I should like to have your opinion. 



The whole is built upon the views that Physical Philosophers 

 have been lately coming to — that Light, Heat, Electricity, Mag- 

 netism, Chemical Affinity, and Mechanical Motion, are all to be 

 regarded as forms or modes oi force, and that they are mutually 

 convertible, each being capable of producing the rest, either 

 directly or through the medium of electricity, which is a sort of 

 connecting link among them all. Thus the friction of two 

 similar bodies produces heat ; of two dissimilar, electricity ; the 

 heat and the electricity being more abundant as the motion is 

 retarded, i.e. as the friction is greater. Conversely heat and 

 electricity may be made to produce mechanical motion, as in 

 the steam-engine and in the various electric rotatory machines. 

 So electricity will produce heat, and heat will generate electricity. 

 Electricity and magnetism are not identical, as was once sup- 

 posed ; but each will produce the other, or may be converted 

 into it. And, as in all these cases, the agent and the product 

 are in a constant proportion to each other, it seems as if 

 the same force were everywhere in action, though varied in its 

 manifestations according to the circumstances under which it is 

 operating. 



Now, I was first led to apply these views to the Vital forces 

 by the very close relation that exists between nervous agency 

 and electricity. All the most recent and trustworthy experi- 

 ments lead to the conclusion that the two are not identical, as 

 some have supposed, but that they are very closely related; 

 Electricity being able to generate Nerve-force (manifested both 

 in musculoj motion and in sensation), and Nerve-force being 

 able to generate electricity, as in the electric fishes. Carrying 

 out these views, I have brought together phenomena which in- 

 dicate that the Nerve-force may be excited by Heat, Light 



