162 PICKERING. — LUNAR AND HAWAIIAN PHYSICAL FEATURES COMPARED. 
On the Moon the height of the outer wall is roughly proportional to the diameter 
of the crater. For a crater whose diameter measures 30 to 40 miles, the height 
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of the outer wall is usually about one mile. For a crater a mile in diameter its 
height would be 150 feet. Dividing this figure by 6, the correction for gravity 
mentioned at the beginning of this paper, we find 25 feet to be the theoretical 
height for a terrestrial crater a mile in diameter, thus agreeing with the figure 
above given. 
In April, 1879 a silent discharge from the crater occurred, the lava apparently 
making its escape out at sea. A few months later activity was again resumed, the 
crater becoming extremely active in 1880. A. J. S., CXVIII, 227 ; CXX, 72. 
On March 6, 1886, Halemaumau was again emptied. It was a silent disch 
© 
like its predecessor. For several days the surrounding walls continued to fall into 
the pit. A month 
deepest portion had the shape of an inverted cone 
whose apex was 570 feet below the floor of Kilauea. Three months after an erect 
cone was found formed of loose blocks, and measuring 150 feet in height. During 
the next two years this cone gradually floated upwards, no additions being made 
summit 
beneath 
This action seems to have been due to the pressure of the lava 
The rate of elevation was about three inches per day. A. J. S., CXXXI, 
397 ; CXXXVII, 48. 
The next discharge of Halemaumau occurred on March 6, 1891. It was accom- 
panied and followed by a series of light earthquake shocks, but otherwise it was a 
quiet discharge. Prior to this date the pit contained a central cone with three lakes 
surrounding it, one east, one west, and one south. The direction of the current on 
the surface of these lakes in each case was away from the cone. The cone which con- 
sisted in part of several peaks rose to a height of at least 200 feet above the lakes. 
As-seen from the Volcano House about one-third of its height was above the western wall 
of Kilauea. The structure of these peaks was loose, and sulphurous vapors escaped 
from their whole surface. The fire fountains on the lakes sometimes played obliquely, 
and without the emission of steam. On the evening of March 6, at 9:30, a light earth- 
quake shock was felt, and the peaks settled slightly ; the next morning they were out 
of sight. A month later in place of the peaks and lakes an empty pit was seen, 
measuring half a mile in diameter. The walls were vertical and 500 feet in depth. 
Soon after this the lava reappeared in the bottom of the pit, and by the end of April 
a lava lake 100 to 200 feet in diameter had formed. A year later the diameter of 
the lake was a little over 800 feet. It was then very active, as many as fifteen fire 
fountains having been counted at one time. It was probably at about this time that 
