LUNAR AND HAWAIIAN PHYSICAL FEATURES COMIWKKI) 
! 
The lunar surface presents such a strong contrast to the more thickly populated 
portions of the Earth, that little resemblance between them can be traced. It has 
therefore naturally proved very difficult to explain the nature and origin of many of 
the features of our satellite. Even those of our volcanic regions which have been 
most extensively studied, show little analogy to the Moon. There are other regions, 
however, notably in the Hawaiian Islands, where an entirely different class of volcanic 
phenomena are exhibited. These it is now found bear a striking resemblance in some 
respects to what we find upon our satellite. Although the Hawaiian craters are mostly 
extinct, or at present inactive, yet they are the only ones known of this type exhibit- 
ing any activity whatever. 
In view of these facts the writer determined to visit the Hawaiian Islands in the 
summer of 1905, and study their volcanic features with especial reference to those 
found upon the Moon. In Hawaii a considerable number of the craters are of the 
engulf ment type, as distinguished from those of the explosive type, so well developed 
in southern Europe. In the latter class a high truncated cone is built up by mild 
eruptions of steam and cinders, sometimes alternating with lava. At long intervals 
violent explosions occur, which sometimes blow away a large portion of the summit, 
thus entirely changing the shape of the mountain. Such an explosion of steam 
occurred in Vesuvius at the time of the destruction of Pompeii, and a still more violent 
one in Krakatoa in 1883. Nothing whatever of this sort is found upon the Moon. In 
volcanoes of the engulf ment type on the other hand, comparatively little steam is 
evolved, often there is no exterior cone, and the craters enlarge quietly by the crack- 
ing off and falling in of their walls. 
The Hawaiian structures, although similar to those of the Moon, are comparatively 
on a very small scale, and their dimensions must often be multiplied by a factor of 
from 100 in the case of the older craters, to 300 in the case of the more recent ones, 
in order to equal the dimensions of the similar formations found upon our satellite. 
This applies especially to horizontal distances, — vertically a factor of from 10 to 
20 more nearly represents the proper proportion. 
