482 Intelligence and Miscellaneous Articles. 



analogous to ethyl, easy to observe distinctly, exist, and at a low 

 temperature, between the Sun's atmosphere and our own. The 

 observations made in America by Prof. Langley with his bolometer, 

 although made for a totally different purpose, tend to confirm the 

 results obtained by Capt. Abney upon the Eiffel. We may also 

 add to these proofs the interesting observation of Prof. Schwedoff 

 (still unpublished, and communicated to me on the same occasion 

 by Prof. Silvanus Thompson), according to which large hailstones 

 of cosmical origin have sometimes fallen upon the earth. This 

 observation, however, needs to be confirmed. 



Accepting these observations as founded upon facts, physical 

 considerations are not wanting for the approximate determination 

 of the actual density of the stellar vapour, which, in this case, is 

 only a function of the temperature of space. As Gorschow, on 

 30th November 1871, observed a temperature of — 63° C. in the 

 Arctic regions, it follows that the stellar medium (which, if it con- 

 sists of a vapour, must be able to intercept calorific rays) must be 

 at a temperature comprised between — 63° and the absolute zero 

 (— 273°) ; the solar radiation must maintain in it some temperature, 

 or, at least, such a temperature that the dissociation of this medium 

 is very active. 



It is to Regnault that we owe our most exact knowledge of the 

 density of vapours at different temperatures ; but his researches did 

 not extend below —32° C, and his formulae cannot be rigorously 

 applied below that point ; nevertheless they enable us to estimate 

 approximately what may be the densities of a vapour at lower 

 temperatures ; and it is thus that we are led to believe that at 

 — 130° the density of aqueous vapour does not exceed 5,000,000 

 atmosphere. If we assume, further, that the gaseous mass which 

 fills space contains only ^ of aqueous vapour, the other four fifths 

 being composed of hydrocarbons, carbonic acid, and nitrogen, the 

 total pressure of the vapour would not exceed 1,000,000 atmosphere. 



These vapours would traverse space with a velocity equal, pro- 

 bably, to half the tangential velocity at the surface of the Sun, or 

 at about 1 kilometre per second. It would be easily demonstrated 

 that a column of these dissociated gases travelling with this velocity 

 towards the polar surfaces of the sun and .taken at a distance of 

 5,500,000 Idiom, from the Sun (equal to the mean distance of 

 Mercury, the nearest of his planets) would present a section of 

 flow towards the Sun equal to 140,000 milliards of square kilometres, 

 much more than sufficient to furnish the material necessary to 

 yield by combustion the heat required to maintain the solar radi- 

 ation. 



Perhaps the eminent Director of the Bureau des Longitudes 

 may be inclined to think that a gaseous medium of a density equal 

 at most to 1,000,000 °f taat °f our atmosphere might still interfere 

 with planetary movements to a degree incompatible with the facts 

 ascertained by astronomical observations. If this be the case, it 

 would suffice to assume a still lower temperature for this medium, 



