1867.] 



of Electinc Energij. 



411 



of tlie media by which the several modes of motion are transmitted. It is 

 unquestionable that sound-waves are transmissible by all kinds of matter ; 

 but can any valid reason be assigned in favour of the still prevalent opinion 

 that other modes of wave-motion are incapable of transmission by ordinary 

 matter ? — this incapacity being implied in the adoption of the self-contra- 

 dictory hypothesis of an imaginary medium, not cognizable by any known 

 means of perception. 



It is a remarkable fact that in all the superseded crude notions of physical 

 causation, each phase of physical energy has been presented in the garb 

 either of impalpable, imponderable (in fact immaterial) matter itself, or of 

 the vibrations thereof ; and to some of these hypotheses have been suc- 

 cessively added some violent supplementary hypothesis, in order ade- 

 quately to meet the requirements of advancing knowledge. 



To begin with chemical action : — What are now universally recognized 

 as simple metals were once supposed to consist of some earthy matter (their 

 oxides) combined with *' Phlogiston," — the material principle of briUiancy. 

 But, unfortunately for the theory, it was soon found that the metals, on 

 parting with their share of phlogiston {i. e. becoming oxidated), not only 

 did not lose any, but actually acquired weight; therefore phlogiston 

 was assumed to be not only imponderable, but A?/^e?*-imponderable — 

 i. e. endowed with the property of absolute levity, or negative weight ! 



In the next place, the Newtonian theory of light assumed light to 

 consist of molecules (of course imponderahle') emanating from the source 

 of light, and impinging on the perceptive organs of vision. But this 

 hypothesis would not fit the phenomena of diffraction and interference ; 

 and to suit these physical facts the molecules must either be thrown into 

 periodical "fits" of transmission or reflection, or the ray must be a row 

 of egg-shaped molecules perpetually making isoperiodic somersaults, and 

 plunging into a medium if they come on their heads, or bounding off if 

 they fall against it sideways. Then, again, heat was supposed to consist of 

 material particles emanating from the source of heat ; and as a ball of ice 

 placed in one focus of a concave mirror was found to lower the temperature 

 of a thermometer placed in the conjugate focus, there were assumed to be 

 particles of cold, as well as of heat : it is needless to add how completely the 

 theory of exchanges accounts for these facts. At length these wild specula- 

 tions were superseded, and light and heat were admitted into the category 

 of wave-motion ; but electricity and miagnetism were still supposed to be 

 either single or dual forms of " fluid " matter ; and 



(•' Saxa etiam niolli clui*a teruntiu' aqua ") 



these "fluids" are probably still running in the deep channels they have 

 worn in some philosophic minds. 



But the principle of admitting imponderability into the category of 

 legitimate physical hypotheses had become tacitly accepted ; and the 

 conclusion was at once jumped at by the authors of the undulatory theory 



