1908] on the Scientific Work of Lord Kelvin. 213 



which are imposed on reversible phenomena by the principle of the 

 conservation of energy. The demonstration on these lines that there 

 can be no rotational quality in either magnetic or dielectric excitation 

 in continuous media afterwards became, in Maxwell's hands, one of 

 the main confirmations in the general electric interpretation of optics, 

 by leading at once to the validity of Fresnel's theory of double 

 refraction. 



But we must return from this digression. The cosmical aspect 

 of Carnot's principle, in its reconcilement with that of Joule, had 

 immediately arrested Thomson's attention, and the fundamental law 

 of Dissipation of Energy in natural phenomena stood revealed in a 

 brief note in April 1852, embodying the following momentous and 

 carefully formulated conclusions : — * 



" 1. There is at present in the material world a universal tendency 

 to the dissipation of mechanical energy. 



"2. Any restoration of mechanical energy, without more than an 

 equivalent dissipation, is impossible in inanimate material processes, 

 and is probably never effected by means of organised matter, either 

 endow^ed with vegetable life or subject to the will of an animated 

 creature. 



" 3. Within a finite period of time past, the Earth must have 

 been, and within a finite period of time to come the Earth must again 

 be, unfit for the habitation of man as at present constituted, unless 

 operations have been, or are to be, performed, which are impossible 

 under the laws to which the known operations going on at present 

 in the material world are subject." 



It is of interest to contrast this principle of degradation, or 

 diffusion, of energy towards a uniform equilibrium, with the other 

 great principle, dominating the phenomena of the organic world, 

 whicii took shape at about the same time. Just fifty years ago 

 biological thought was startled with the idea of the gradual evolu- 

 tion of organic forms, by the persistence, through hereditary trans- 

 mission, of such accidental modifications as are adapted to the sur- 

 rounding conditions of life, to the existing environment. In inorganic 

 phenomena the energy becomes distributed among merely passive 

 molecules ; in the organic world the unit of investigation is an 

 organism which has apparently the active property of fixing and 

 transmitting in its descendants any structural peculiarity that it may 

 come by. But even here there is something in common ; the auto- 

 matic evolution towards improved adaptation, in this case with no 

 limit or equilibrium yet in sight, is attained at the cost of compen- 

 sating dissipation, namely, the destruction of the individuals that 

 happen to be ill adapted even though in other respects superior. 



We observe in passing that in Thomson's formtilation. Clause 2 

 already implies Olausius' conception (185-1) of compensating trans- 



* Log. cit., p. 514. 



