1875.]  Selenography : its Past, Present, and Future. 211 
attached to the name of the nearest important forma- 
tion. 
Madler’s instrument was a Fraiinhofer achromatic of 
3% inches aperture, and though smaller than Lohrmann’s, 
yet probably of finer quality, its excellence being apparent 
from its admitting commonly of a power of 300 being used 
for drawing the lunar details, but its moderate aperture 
possesses important bearings on many of the results given 
in Beer and Madler’s ‘‘ Der Mond,” where the influence of its 
want of capacity for dealing with the more delicate phe- 
nomena is often exhibited. There can be no question, 
however, of the great advance on all its predecessors of the 
** Mappa Selenographica,” not only from the vast amount of 
detail for the first time shown, but in its general accuracy, 
owing to its being based on the result of actual measures. 
Though deficient in minuter detail from the small aperture 
of their instrument, and though not implicitly to be trusted 
on the more delicate features, yet in its general fidelity the 
“* Mappa Selenographica” is superior, not only to all its pre- 
decessors, but likewise to its successors. 
Upon the conclusion of Beer and Madler’s great work, it 
was generally considered as established that the great ques- 
tions in connection with the condition of the moon were 
finally settled, with the exception of the reason why volcanic 
action had produced such different effects on the moon and 
earth, and the real origin of some of the more inexplicable 
formations, principally the great ray or streak systems, and 
the rills or clefts, whilst it was considered certain that the 
moon was to all intents an airless, waterless, lifeless, un- 
changeable desert. With this opinion prevalent, the natural 
effects of such great works as Beer and Madler’s shortly 
ensued ; the attention of astronomers was directed to other 
fields, and selenography, resting on its laurels, made no 
further progress for many years; and until 1865 Schmidt, 
at Athens, may be regarded as the sole selenographical 
worker on an adequate scale. 
The only point in connection with lunar physics that during 
this period excited attention was that of the real libration 
of the moon, and was due to the investigation of Bessel. 
In a memoir in the ‘‘ Ast Nach,” in 1839, he entered into an 
examination of the question of the moon’s real libration, as 
presented by the theoretical investigations of Lagrange, 
Laplace, and Poisson, and pointing out the uncertainty 
attending the value deduced by Nicollet. As a basis for 
further investigation, he deduced the position of the crater 
Mosting A by two careful measures with the Konigsberg 
