at the total solar Eclipse in 1882 



the state in which it emits as much energy as it absorbs, so 

 that its effective power of absorption would be ;'/? 



I do not ask these questions lightly. The subject has 

 occupied my attention off and on for the last eighteen years, 

 and I believe that the only answer to them is that the value 

 of tJie solar constant which is now accepted is very mucli 

 exaggerated. This view is, I think, supported by the follow- 

 ing consideration. 



Taking the length of the sun's radius as unity we have in 

 the accompanying table the distance (d) from its centre to 

 the sun's surface, and to the three inner planets, Mercury, 

 Venus, and the Earth, and the squares of these distances (d-}. 

 The squares of the distances represent the area on each planet 



over which the radiation per unit area of the sun's surface is 

 spread. It will be seen that the area on the earth's surface 

 covered by the radiation from a given area of the sun's surface 

 is almost double that covered by the same radiation on the 

 surface of Venus, and therefore the intensity of radiation on 

 Venus is almost exactly double that on Earth. In other 

 words, the true value of the solar constant at a point on the 

 orbit of Venus is almost exactly double its true value at a 

 point on the Earth's orbit. It is impossible to believe that 

 the cloudless atmosphere of the Earth, the whole mass of 

 which is only I kg. per sq. centimetre, can produce an absorb- 

 ing effect equal or superior to the dissipating effect of such 

 a distance as that separating the orbits of Venus and the 

 Earth. 



To conclude, it has been shown that under favourable 

 meteorological and geographical conditions, by the use of 

 ordinary and necessarily imperfect mechanical appliances it 

 is possible to collect from a square metre of surface exposed 

 perpendicularly to the sun's rays 8888 gr. C. of heat which 



