Intelligence and Miscellaneous Articles. 401 



It is perfectly true that, for the physicist, air at ¥0 ^ would be 

 an almost absolute vacuum, so much so indeed that in such a 

 vacuum the electric spark would no longer pass. But to the 

 astronomer such a medium would be very dense. When we 

 speak, in Astronomy, of the resistance of a medium or of the 

 aether, and when by the aid of the most delicate observations and 

 the most profound calculations, we seek for traces of this re- 

 sistance, we have to do with a very different thing. 



Without entering upon these discusions, I will remark that the 

 trajectory of a cannon-ball with a velocity of 500 m. is sufficiently 

 altered at the end of a few seconds to compel artillerists to take 

 into account the resistance of the air in their tables. 



If the air is reduced to ^gW' Du,; tne velocity of the projectile 

 becomes that of the celestial movements, 60 times as much for 

 example, these palpable effects will become, for a multitude of 

 celestial projectiles of dimensions comparable to those of our 

 cannon-balls, twice as great as in our firing-grounds, and this not 

 merely at the end of a few years or a few centuries, but at the 

 end of a few seconds. 



In the second place, it seems to me that the celebrated English 

 physicist has somewhat neglected to examine into the quantity of 

 matter which he adds to the solar system. Under the influence of 

 attraction this matter would go to unite itself with the preexisting 

 stars, with the sun especially, and would continually augment their 

 mass. Nothing is easier than to form an idea of this. A litre of air 

 containing the required proportion of aqueous vapour weighs at least 

 1 gr. at the ordinary pressure. At a pressure of yoTTQ this will be 

 0-0005 gr., and a cubic metre will weigh 0*0005 kilog. This being 

 settled, if we restrict the solar system to a sphere including all 

 the planets as far as Neptune, the weight of the excessively rarefied 

 matter added by the hypothesis would be, in kilogrammes, 

 1 7T (6400000 x 24000 x 30) 3 x 0-0005 kilog. * 



The actual weight of the Sun is, in kilogrammes, 

 1 7T (64000000) 3 x 5-6 x 324000 1. 



The first is 100,000 times as great as the second. It is there- 

 fore 100,000 times the mass of the Sun that this hypothesis adds to 

 those of which celestial mechanics has hitherto kept so minute an 

 account. 



It is not very probable that the astronomers will adopt such 

 hypotheses. No doubt they would be pleased to think that Nature 

 has provided the Sun with resources to make his heat last longer ; 

 but as his final refrigeration is still, under any circumstances, a 



* The first number is the radius of the earth in metres ; the second the 

 distance of our globe from the Sun in terrestrial radii; the third the 

 distance of Neptune in parts of the distance of the Sun. 



t The first number is the radius of the earth in decimetres ; the second 

 the mean density of our globe referred to that of water - the third the 

 mass of the Sun referred to that of the earth. 



