TWENTY-EIGHTH ANNUAL MEETING. el 
masses, a trend toward that one was set up, and the impacts or collisions thus 
produced not only fused the striking meteorite but also that portion of the nu- 
cleus that was struck. A coalescence took place, the central body grew in size, 
and its power of attraction increased accordingly. In harmony with the laws of 
celestial dynamics, the velocity of the moonlets toward the central controlling 
mass would increase, and the energy expended would be sufficient to melt every 
moonlet, even though it should be composed of the most refractory substance. 
The portion of the surface of the central mass struck by the moonlet would itself 
be fused, and there would be formed a cup-shaped depression similar to the crater 
forms now seen upon the Moon, together with their attending phenomena. The 
larger the moonlet, the larger and deeper would be the depression and the greater 
the fusion of the rock material. The smaller the moonlet, the shallower would 
be the crater’s depth, and less its diameter. I have seen in the cuts and gullies 
made by the overflow, and backwater, and subsequent subsidence, of the San 
Pedro river in southern Arizona, the plastic mud deposited by the falling waters 
of such consistency, that when a pound or two-pound rock was dropped into that 
mud, an examination of it next day showed a crater-like form resembling exactly 
the forms of the lunar craters, taking the normal type as an example. 
‘* Tf a drop of water be made to fall on a still surface of water, the outward- 
moving annular wave at one instant inclosesa crater; at the next instant amound 
rises in the center of thecrater.’’ In the case of the viscous mud, as shown in the 
example of the San Pedro, if a stone fall from a certain height, ‘‘ a cup-like cavity or 
crater with a smooth rim will be produced ; if it fall from a greater height it will 
produce a larger cup with smooth rim and smooth dome-like hill in the center.”’ 
An experiment of this sort can easily be performed. The white streaks, consti- 
tuting one of the great lunar features, is by this theory of impact also accounted 
for. According to Dr. B. A. Gould, ‘‘The most remarkable appearance of the 
Moon, for which nothing on Earth furnishes an example, is presented 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 extending 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.’’ Accepting the premises on 
which the ‘‘ meteorite theory ’’ is based as true, all the characteristics of the 
Moon’s surface — craters, streaks, central domes, rising from the floors of the 
craters, and even the building of the Moon itself —can be explained on the 
theory of the impact of moonlets or meteorites upon the central mass. 
But it may be stated that the impact of the larger masses upon the central 
one, in order to produce results such as we see on the Moon’s surface, is a theory 
that contains inherent and radical difficulties. The diameter of the Moon is 
about 2,100 miles, and by this theory we have a moonlet whose impact was ca- 
pable of producing a crater 800 miles in diameter. We may reasonably suppose 
that when the lunar ring was broken into fragments, the central mass may not 
have had a diameter of over 1,000 miles and collisions would take place not long 
after the dismemberment. A collision between two bodies, one 1,000 miles in 
diameter and the other 800 miles in diameter, would break both bodies intoa 
multitude of smaller bodies, and hurl them outward into space in a thousand dif- 
ferent directions. This process would be carried on just as fast as the meteoric 
masses of the old ring should be drawn towards the center. A swarm of aster- 
oids would therefore, under such conditions, have taken the place now occupied 
