THE MOON. 
62 1 
tlie Observatory to be continued. Enough, however, was seen to 
prove the omission of several details in the best maps. We 
may ventm*e to say that the immense labour of Argelander, in 
his maps of the stars, extending to the faintest classes, is 
scarcely so difficult as in portraying the caves, craters, moun- 
tain-ridges, and stratifications of the lunar surface. Even in 
the map projected by the British Association, we must remain 
content with drawings of the various parts as seen with dif- 
ferent instruments. If the portion thus observed be viewed 
with higher powers, new features will be seen. Thus, the 
interior of a mountain viewed through Earl Rossers great- 
est telescope was found covered with a number of minute 
blocks, which were invisible in the three-foot mirror. It would 
thus be unfair to compare the pictures taken by different 
instruments, or even with the same instrument by different 
observers. It is very probable that the idea of actual changes 
takingplace on the moon arises from these circumstances. Mr. 
Webb, who has devoted great attention to this subject, believes, 
however, in actual physical alteration of surface, or of obscm*ation 
arising from volcanic action or by changes in a possible lunar 
atmosphere, — a suggestion due to Schroeter. It is to be 
remembered, that it is only in the most minute details that 
those changes have been perceived. Mr. Webb thinks that 
the eruptions lying between Copernicus and Eratosthenes have 
taken place during the present century ; but this opinion is 
derived solely from a comparison of the maps of Schroeter 
and Gruithuisen ; and the other changes mentioned by him are 
founded on similar grounds. It may be mentioned incidentally, 
that Maedler reckoned 20,000 craters on the moon^s surface 
as visible in his telescope of four-inch aperture; and the 
patience necessary for mapping those may easily be imagined. 
Perhaps the beautiful photograph of Mr. De La Rue may be 
brought to such a state of perfection as to give all the minutise 
visible on the lunar surface, as that eminent observer has 
already completed one whose diameter is comparable with that 
of the large map of Maedler. Until a much more searching- 
scrutiny has been made, judgment must be suspended on 
chauges in the moon. The ^Afills ” already mentioned in the 
interior of Gassendi, which were detected by the writer in 
1854, might be taken as decided marks of change, because not 
seen in previous charts. But it has since been found that they 
were already seen by Maedler many years before that time, 
only that they were discovered subsequently to the publication 
of his large map, and making use of the great Dorpat 
telescope. 
2 T 
VOL. IV. NO. XVIT. 
