176 PICKERING. — LUNAR AND HAWAIIAN PHYSICAL FEATURES COMPARED. 
expelled from the openings of the spiracles in the central peaks themselves. The 
valleys seem to be flat bottomed, which would imply the action of ice rather than 
water. Indeed, at the present time the central peaks of Theophilus are of a dazzling 
brilliancy as compared with their surroundings. This, it is believed, is due to ice. 
The floors of both Theophilus and Copernicus show ridges that may be lateral 
moraines. 
What we ordinarily speak of as the lunar day is twenty-nine and a half terrestrial 
days in length. From the standpoint of climate it may quite as properly be called 
the lunar year. In the latter case sunrise corresponds to spring, and sunset to 
autumn. The interval between them is very nearly fifteen of our days. Using the 
terms in this sense, we find that there are numerous spots scattered over the surface 
of the Moon which as the season progresses gradually darken. They reach their 
maximum development about or soon after midsummer, and from thence on slowly 
fade out and disappear with the approach of autumn. They are widely distributed 
over the surface, excepting near the poles, but develop most rapidly in the equatorial 
regions. It is believed that these variable dark spots are due to vegetation. 
One of them is seen in the northern part of Julius Csesar, the large crater just 
north of the Ariadaeus rill, Figure 29. Others are found to the north and east of it. 
The summer temperature on the Moon is about that of our desert regions at midday. 
The winter temperature approaches absolute zero, but since grain and other seeds 
have been exposed without injury to the temperature of liquid air, it seems clear that 
even terrestrial vegetation can stand a range of temperature quite comparable to that 
found upon the Moon. 
The central area of Figure 35 represents the crater Eratosthenes taken at the time 
moon. On the photograph it measures an inch and a quarter in diameter, and 
is on a scale of ^shs*, or thirty-two miles to the inch. The central peaks are pure 
white, and cover an area about one quarter of an inch in diameter. Northeast and 
northwest of them are two dark spots upon the floor, and southeast of the peaks is a 
very dark area lying partly on the floor and partly on the inside wall. These spots 
go through various interesting changes in density as the season progresses, at 
times entirely disappearing. In one place a slow movement of progression at the 
rate of four feet per hour has been noted. Outside of the crater, large dark areas 
are seen, which do not, however, lend themselves so readily to measurement as do 
those within it. Two dark lines lead away from each of the spots at the base of the 
central peaks. These lines are believed to be anal, 
of full 
Mars 
© 
the so-called canals of 
