6 Physical Changes upon the Moon's Surface . [January f 
lunar observations, and especially the latter, as he repeatedly 
drew this particular part of the moon. In the drawings of 
Schmidt, however, whenever this crater Linne is shown, it 
is as a deep crater, entirely in accordance with the descrip- 
tion of Lohrmann and Madler. 
In October, 1866, however, Schmidt was startled by 
finding no trace of Linne, when it was in a position when 
it should have been most conspicuous. Instead of the deep 
wide crater with its interior filled with intense black shadow, 
all he could deteCt was a faint, indistinct, cloudy marking, 
about 5 miles in diameter. During the subsequent evenings 
it retained this aspeCt, though at times it was so indistinct 
as to be barely visible. Schmidt immediately announced 
this startling circumstance, and during the end of 1866 and 
the commencement of 1867 nearly every astronomer in 
Europe directed his attention to this now-celebrated spot. 
Since then this portion of the moon has been repeatedly 
examined by selenographers, but Linne has never been seen 
of the size and character ascribed to it by Lohrmann, 
Madler, and Schmidt. The conspicuous deep crater has 
utterly disappeared. 
In what manner is this change to be explained, and how 
is it that apparently so unmistakable an instance of physical 
change has been rejected as not established ? These ques- 
tions are best answered by describing what has been seen in 
the place formerly occupied by the deep crater. Where 
Linne was, it has been already mentioned, an indistinct 
white cloud-like mark was seen ; but powerful telescopes 
and assiduous examination soon revealed something else. 
When first the sun illuminated the region containing Linne 
a small conical mountain peak was detected, this mountain 
being about 100 to 200 feet high, and casting a short black 
shadow, and was by some mistaken for a small crater. 
Subsequently other observers detected a minute crater cone. 
When first seen it was estimated by Schmidt to be about a 
quarter of a mile in diameter, and by Secchi, of Rome, and 
Buckingham as about one-third of a mile across ; this crater 
lying to the west of the small hill. If the estimates of 
these earlier observers are to be trusted, and Schmidt at least 
was not likely to be mistaken, a most important circumstance 
must have occurred ; for when next seen the crater was nearly 
three times as large, or nearly 1 mile in diameter, according 
to D’Arrest of Copenhagen, Schjellerup, Huggins, and Wolf. 
In July, 1867, the crater was sufficiently large and distinct 
to permit of its being measured, and according to Hugginsit 
was rather under 2 miles in diameter—a result confirmed, 
