242 
GILBERT. 
he has found it convenient to give them many distinctive 
names; * there are thousands of bright streaks, which are 
neither ridges nor hollows, but mere bands of color; there 
are many hundred narrow linear depressions, which he calls 
rills. 
Despite the persistent enthusiasm, the patience, and the- 
industry with which he has studied his field, it must never¬ 
theless be admitted that he has rarely satisfied himself and 
never satisfied his fellow-workers with the explanations he 
has suggested as to the origin^of the features his map de¬ 
lineates. But selenographers are not the only students of 
the moon’s face. There are also selenologists, who use the 
telescope comparatively little but cogitate much, and who 
have evolved theories of great ingenuity and variety. Far 
be it from me to say aught to their disparagement, for this 
evening I join myself to their ranks; but, again, it must be 
confessed that the selenographers do not look upon the teach¬ 
ings of the selenologists with favor. So, despite all that has 
been done, the field of theory is still open, and this is my 
excuse for putting forth ideas founded neither on protracted 
observation f nor on protracted study—this and the further 
plea that the problem is largely a problem of the interpreta¬ 
tion of form, and is therefore not inappropriate to one who 
has given much thought to the origin of the forms of terres¬ 
trial topography. 
Crater Characters .—In the study of lunar physiography— 
or physiognomy, if you prefer—interest naturally centers in 
the craters, for these are the dominant features. All theories 
begin with them ; and, before examining the theories, it will 
*Neison classified craters as crater cones, crater pits, craterlets, craters 
proper, crater plains, ring plains, mountain rings, and walled plains, 
recognizing gradation between them and also between walled plains and 
maria. The Moon and the Condition and Configuration of its Surface,, 
by Edmund Neison, London, 1876. 
t My observations were practically limited to two lunations in August, 
September, and October, 1892, a period affording eighteen nights available 
for work. My instrument was the 26|-inch refractor of the United States 
Naval Observatory, and the power found most serviceable was 400. 
