454 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 13, No. 21 
The specimens of lava that Preston collected at Mauna Kea were 
examined by Merrill,> who determined the specific gravities of four- 
teen of them, the average being 2.63. This is very low and is ac- 
counted for by the fact that many of the specimens were vesicular 
or not fresh, as pointed out by Merrill. From his pendulum obser- 
vations and estimates of the altitude and radius of the base of the 
mountain, Preston calculates the value 6 = 0.5654; in which 6 is 
the average density of the rocks and A is the average density of the 
Earth. The value given is the mean between those arrived at on 
the assumption that the attraction of the mountain is the mean 
between that of an infinite plane and of a cone. Using Merrill’s 
average specific gravity the mean density of the Earth is, therefore, 
calculated to be 4.655, a figure far below the accepted value. Preston, 
however, does not use Merrill’s data alone but combines these with 
the specific gravities of lavas from Mauna Loa and Kilauea, as deter- 
mined by E. 8. Dana.* He thus arrives at the average Mauna Kea 
rock specific gravity 2.90 and the value 5.13 for the mean density of 
the Earth, this last being also much below that generally accepted, 
which may be taken as 5.52.” 
I determined the specific gravities of nine specimens of the Mauna 
Kea rocks, some of whole hand specimens with the balance and others 
of the rock powder with the pycnometer.* The results, with two 
determined by Daly,® are given in Table I, with the calculated densi- 
ties. The specific gravity No. 1 (2.870) is a new determination of 
that of the andesite of Laupahoehoe, the previously published value ; 
(2.709)'® having been too low because of the vesicularity of the speci- 
men. No. 10 (2.959), of the olivine basalt of Kaula Gulch, is also 
new. ‘These results give an average specific gravity of 2.969 and an 
average density of 2.963; hence, using Preston’s value A = 1.776, 
A = 5,245, This is much higher than the value (4.655) obtained from 
the specific gravities of Preston’s specimens, and somewhat higher 
than that (5.13) calculated by Preston, but is still much below the 
generally accepted value. 
Regarding these results some comment is called for. Preston 
seems to have selected more or less vesicular specimens because he 
°G. P. Merrill in Preston, op. cit., 630. 
6K. 8. Dana, Amer. Journ. Sci. 37: 441. 1889. 
"Cf. the value (5.525) selected by Burgess (Boys in Glazebrook, op. cit., p. 285); also 
Williamson and Adams, Journ. Washington Acad. Sci. 18: 413. 1923. 
® The pyenometer determinations on the rock powder are consistently higher than 
those made on the hand specimens. 
*R. A. Daly, Journ. Geol. 19: 208 and 301. 1911. 
10H. S. Washington, Amer. Journ. Sci. 5: 490. 1923. 
