Lunar Atmosphere, 49 



atmosphere. It has been attempted to establish its existence 

 both by observations, and by arguments of an entirely different 

 nature. Schroeter imagined that he perceived traces of twi- 

 light in that part of the moon which was dark, and principally 

 alorfg the obscure border, which may be seen when the lunar 

 crescent is reduced to a small luminous thread. According 

 to his observations, he has calculated what the thickness of the 

 moon's atmosphere should be, and found it amounted to a 28th 

 part of the Earth'^s atmosphere. Melanderhjelm has endeavour- 

 ed to demonstrate, theoretically, that the thickness of the atmo- 

 spheres of two celestial bodies should be proportional to the 

 square of the power of gravity at the surface of these bodies, 

 which would give to the lunar atmosphere j^th part of that 

 of the Earth ; but his conclusion should be limited by this con- 

 dition, viz. the universal existence of atmospheres. 



M. Bessel has demonstrated (Astr. Nachr., No. 263) that 

 after attributing the greatest possible altitude to the moun- 

 tains behind which stars in a state of occultation disappear, say 

 24,000 Fr. feet, as also allowing the greatest possible effect 

 which can arise from refraction, viz. a difference of 2'' between 

 the diameter of the moon according to direct measurement, 

 and its extent deduced from the duration of the occultation ; 

 and by still further admitting that the temperature was at 32^ 

 Fahr» from the surface of the moon to an altitude of 24,000 

 Fr. feet : still with all these concessions, of all others the most 

 favourable for the extent of the lunar atmosphere, yet its 

 thickness would amount to only ^ J^th part of that of our at- 

 mosphere, supposing that the two were of the same nature. 

 Upon the supposition that the temperature and the composi- 

 tion of the atmosphere are different, still the results are analo- 

 gous. Thus, supposing it was oxygen gas, the greatest thick- 

 ness would only be ^Jyd part, and it would be j J^th part with 

 a temperature of about minus 240*" R. If it is moreover con- 

 sidered that the stars, on reaching the obscure edge of the 

 moon, always disappear suddenly, and without the slightest 

 diminution of their brilliancy, the only conclusion which re- 

 mains, is, that the moon possesses no atmosphere at all compa- 

 rable with ours. 



Concerning the alleged twilight, observed by Schroeter, this 



VOL. XXV. NO. XLIX. JULY 1828. D 



