58 
could remain unaffected by intense heat? Mr. W. R. Birt, our emi- 
nent British Selenologist, had considered the question with his charac- 
teristic care. With Herr Althaus, he estimated ‘that the Moon’s 
hemisphere, which was turned towards the earth, attained at least a 
‘maximum temperature of 840 deg. Fah., upon the assumption that 
its power of absorbing heat equalled that of quartz. The heat thus 
attained would exceed the fusing points of tin and lead, On 
the other hand the minimum temperature of the Lunar night 
he estimated to be—92 deg. Fah., which would give a fall 
of 932 deg. in fifteen days, equal to daily increments and decrements 
of heat of about 63 deg. each.” Mr. Birt had also alluded to the 
very considerable expansions and contractions of the gases (either 
present or liberated) which must attend this enormous variation, 
and suggested that if the heat exceeded the melting points of tin and 
lead it was quite possible that, long before the maximum temperature 
was attained, substances might be fused and vapours given off. The 
Rev- T. W. Webb, who had done more than any other person towards 
popularizing the real study of the Moon, had well said, “‘the action of heat 
is expansive and liquefacient, but not explosive, excepting through the 
sudden dilatation of some elastic material ; and if we find, as we do 
find, evidence of such upheaval and dislocation of heavy substances 
as cannot well be ascribed to mere expansion and pressure, it seems 
difficult to dispense with the presence of aeriform matter suddenly 
liberated from restraint and flashing out its almost irresistible power.” 
The kind of observation generally referred to by those hasty 
writers who assumed the question as long since settled, was that of 
occultations of stars by the moon. Yet, carefully considered, their 
value proved to be merely negative. There were three modes of 
observing them, which were described at length with their results. Of 
the first two, it was shown that there was not a coincidence between 
theory and observation, and it was maintained the discrepancy dis- 
qualified their decisiveness. The third, or spectroscopic, mode was 
especially dwelt upon, and the observations and conclusions of the 
careful and accurate Dr. Huggins shown to be at variance with the 
statements of writers who assumed his work to have disposed of the 
question ; for he had taken the precaution of warning others not to be 
- too hasty in founding opinions upon it. And so the question remained 
open. And we were unable as yet to tell much of a Lunar atmosphere 
at least, 
