THE MOON’S EACE. 
285 
am confident it contains the essence of the theory that will 
finally be adopted. Mr. Wurdemann is one of a number of 
students who have independently advocated the meteoric 
origin of the lunar craters, but his views have never been 
published. In a letter on the origin of the lunar topography, 
addressed by him to Dr. B. A. Gould, occurs the following 
passage: “The most remarkable appearance on the moon, 
for which nothing on earth furnishes an example, is pre¬ 
sented by those immense radiations from a few of the larger 
craters—perfectly straight lines, as though marked with chalk 
along a ruler—starting from the center of the crater and ex¬ 
tending to great distances over every obstruction. My 
explanation is that a meteorite, striking the moon with great 
force, spattered some whitish matter in various directions. 
Since gravitation is much feebler on the moon than with us 
and atmospheric obstruction of consequence does not exist, 
the great distance to which the matter flew is easily 
accounted for.” 
This explanation appeals strongly to the eye. The ray 
systems resemble splashes so closely that it is difficult to 
understand why the idea that they really are splashes has 
not sooner found its way into the moon’s literature. It 
accounts for the straightness of the rays, for their vanishing 
edges and ends, for their independence of topography, for 
their relation to craters, for the whiteness of the associated 
craters, and for the nimbus in w T hich the rays sometimes 
unite close to the crater. It explains the white crests of 
many gray craters, for peaks would intercept more than 
their pro rata of the horizontal shower. 
It raises also a number of questions, the discussion of 
which should throw much new light on the moon’s history. 
What is the white substance ? Why do its traces become 
faint in passing from the bright uplands to the dark plains ? 
Why do wavy lines replace straight ones in the radiation 
from Copernicus? Why do certain great rays of Tycho’s 
system trend toward a point on the rim and not toward the 
center of the crater? Why are several craters, especially 
