THE FUEL OF THE SUX. O 



transmission of electricity affords a means of testing the exist- 

 ence of atmospheric matter with a degree of delicacy of which 

 Wollaston had no conception, we are still unable to detect any 

 indication of any limit to its expansibility. 



The most remarkable part of Dr. Wollaston's paper is the 

 reductio ad absurdum by which he seeks to finally demonstrate 

 the finite extent of our atmosphere. He maintains, as I do, 

 that if the elasticity of our atmosphere is unlimited, its exten- 

 sion must be commensurate with the universe, 1hat every orb 

 in space will, by gravitation, gather around itself an atmosphere 

 proportionarc to its gravitating power, and that, by taking the 

 known quantity of the earth's atmosphere as our unit, we may 

 calculate the amount of atmosphere possessed by any heavenly 

 body of which the mass is known. On this basis Dr. Wollas- 

 ton calculates the atmosphere of the sun, and concludes that its 

 extent will be so great as to visibly affect the apparent motions 

 of Mercury and Venus, when their declination makes its 

 nearest approach to that of the sun. No such disturbance 

 being actually observable, he concludes that such an atmos- 

 phere as he has calculated cannot exist. In like manner he 

 calculates the atmosphere of Jupiter, and finds it to be so great 

 that its refraction would be sufficient " to render the fourth 

 satellite visible to us when behind the centre of the planet, and 

 consequently to make it appear on both (or all) sides at the 

 same time." 



^On examining these calculations, I have discovered the very 

 curious error above referred to. As this is a matter of figures 

 that cannot be abridged, I must refer the reader to the original 

 calculations. I will here merely state that Wollaston's 

 method of calculating the solar gravitation atmosphere and that 

 of Jupiter and the moon leads to the monstrous conclusion 

 that, in ascending from the surface of the given orb, we always 

 have the same limited amount of atmospheric matter above as 

 that with which we started, although we are continually leav- 

 ing a portion of it below. 



Wollaston's mistake is based on the assumption that, under 

 the circumstances supposed, the atmospheric pressure and den- 

 sity, at any given distance from the centre of the given orb, 

 will vary inversely with the square of that distance. As the 

 area of the base upon which such pressure is exerted varies 

 directly with the square of the distance, the total atmosphere 

 above every imaginable starting-distance would thus be ever 

 the same. That this assumption, so utterly at variance with 



