210 Dr. H. Hudson on Wave-Theories of 



repellent^ while the whole stellar system might be kept together 

 by a still higher order of attraction-vibrations resulting from 

 composition of the vibrations from all the individual stars. This 

 theory would receive confirmation if observation should eventu- 

 ally decide that the proper motions of stars are vibratory. 



I have now adverted to the more essential parts of the theories 

 of all the physical forces_, and have endeavoured to account for 

 their modes of action by mathematical arguments founded on 

 the hypothesis that all the forces and their laws are ascribable 

 to pressures of the sether. The extent and comparative facility 

 of the applications of the deductions from this hypothesis in ac- 

 counting for observed facts and laws seem to justify the conclu- 

 sion that it is (to adopt an expression employed by Vrhewell in 

 his ^Inductive Sciences'') ^^the appropriate idea^^ of Physics. 



Cambridge, July 24, 1872. 



XXV. On TVave ^Theories of Light, Heat, and Electricity . 

 By Hexry Hudson, M.D,, M.R.I.A.^ 



THE withering influence w^hich the authority of a great name 

 exercises over the views of men of science is perhaps no- 

 where so strongly marked as in the theory of optics. Tf the 

 genius of Tresnel had not arisen to develope the views of our 

 own Young (to whom we owe not only the idea of ^' transversal 

 vibrations '^ but also the grand conception of the " interference 

 of light ^-'), the emission-theory of the illustrious Newton might 

 have continued much longer to check the progress of true 

 science^ 



Although the undulatory theory may be said now to be com- 

 pletely triumphant, it must still be admitted that there remain 

 certain phenomena which require explanation, and I have loog 

 thought that there is one very v\'eak point in the physical con- 

 ceptions upon which the wave-theory has been founded. 



Kuygheus (in order to explain the phenomena of double re- 

 fraction) assum.ed the existence of a second vibrating medium, 

 consisting of the aether and molecules of matter conjointly \ and 

 i^oung as well as other eminent philosophers have adopted this 

 view. This assumption is, I believe, erroneous. We know that 

 waves of sound in our atmosphere are 10,000 times as long as 

 the waves of light, and their velocity of propagation about 

 850,000 times less ; and even when air has been raised to a 

 temperature at which waves of red light are propagated from 

 matter, the velocity of sound-waves is only increased to about 



* Commniiicated by the Author, having been read in Section A. of the 



Britisli Association, at their Meeting at Liverpool (18/0). 



