1882.] 



On the Conservation of Solar Energy. 



389 



3. That the penetration of the hyphse of the Saprolegnia into the 

 derma renders it at least possible that the disease may break out in a 

 fresh-run salmon without re-infection. 



4. That the cause of the disease, the Saprolegnia, may nourish in 

 any fresh water, in the absence of salmon, as a saprophyte upon dead 

 insects and other animals. 



5. That the chances of infection for a healthy fish entering a river, 

 are prodigiously increased by the existence of diseased fish in that 

 river, inasmuch as the bulk of Saprolegnia on a few diseased fish 

 vastly exceeds that which would exist without them. 



6. That, as in the case of the potato disease, the careful extirpation 

 of every diseased individual is the treatment theoretically indicated ; 

 though, in practice, it may not be worth while to adopt that treat- 

 ment. 



II. " On the Conservation of Solar Energy." By C. William 

 Siemens, D.C.L., LL.D., F.R.S., Mem. Inst. C.E. Received 

 February 20, 1881. 



The question of the maintenance of Solar Energy is one that has 

 been looked upon with deep interest by astronomers and physicists 

 from the time of La Place downward. 



The amount of heat radiated from the sun has been approximately 

 computed, by the aid of the pyrheliometer of Pouillet and by the acti- 

 nometers of Herschel and others, at 18,000,000 of heat units from every 

 square foot of his surface per hour, or, put popularly, as equal to the 

 heat that would be produced by the perfect combustion every thirty- 

 six hours of a mass of coal of specific gravity = 1'5 as great as that of 

 our earth. 



If the sun were surrounded by a solid sphere of a radius equal to 

 the mean distance of the sun from the earth (95,000,000 of miles), 

 the whole of this prodigious amount of heat would be intercepted ; 

 but considering that the earth's apparent diameter as seen from the 

 sun is only seventeen seconds, the earth can intercept only the 

 2,250-millionth part. Assuming that the other planetary bodies swell 

 the intercepted heat by ten times this amount, there remains the 

 important fact that ffff^tf of the solar energy is radiated into 

 space, and apparently lost to the solar system, and only 225000000 

 utilised. 



Notwithstanding this enormous loss of heat, solar temperature has 

 not diminished sensibly for centuries, if we neglect the periodic 

 changes — apparently connected with the appearance of sun-spots — that 

 have been observed by Lockyer and others, and the question forces itself 



