102 THE HAMILTON ASSOCIATION. 
the task of lengthening the bead roll of discoverers already given 
would be easy and pleasant. But to add to this lengthy list were 
needless, if not wearisome. Moreover the names referred to fairly 
indicate the chief sources of positive knowledge concerning the 
moon, and the progressive efforts by which that knowledge has been 
obtained. ‘There is a wide difference between the ‘‘ perspective 
glass” of Galileo, which made the moon look nine times larger, and 
modern telescopes with magnifying powers of six thousand diameters. 
The optical part alone of a great modern instrument costs a hand- 
some fortune, and its mounting and outfit of accessory instruments 
are costly, taxing as they do the resources of mechanical engineering 
and scientific skill. With such well equipped observatories, and the 
accumulated records of a century at command, one might suppose 
that knowledge concerning the moon would be nearly perfect. But 
science moves at a slow pace, and is more bent on gathering facts 
for inductions than in forming crude inductions from imperfectly 
ascertained facts. The man of science has to curb imagination 
tighter than in other days, and has learned to speak on many sub- 
jects with more diffidence than did his predecessors. A hundred 
years ago the elder Herschel believed the moon to be inhabited, 
and after his time a learned man with an excellent telescope and 
keen vision—Gruithuisen, of Munich—wrote a scientific paper, 
entitled, Extdeckune deutlicher spuren der Mondbewohner—discovery 
of clear traces of the moon’s inhabitants. It is not conceivable that 
such a paper could now be written in earnest. Since that paper 
was written such visionary notions have found little credence. ‘The 
work of Beer and Meedler defined the legitimate boundary of lunar 
investigation. 
An object 300 feet high and about a mile long is said to be ap- 
proximately the minimum visible with a modern large refracting 
telescope, with usual low power ocular. With highest oculars, and 
best conditions of observation, a detached object, 40 feet high, pro- 
jecting its shadow on a level surface might be perceptible. Beer and 
Meedler take 314 English miles to be the extreme distance at which 
a person of keen, unassisted vision can distinguish an object 6 feet 
high, and estimate that it would require a telescope to magnify 
51,000 diameters to shew such an object on the moon. Not much 
more than a tenth part of such magnifying power is at present avail- 
