the mean Denjity of the Earth. 783 
that is to fay, the mean denfity of the whole earth is 
about 44 times the denfity of water. 
To what ufeful purpofes the knowledge of the mean 
denfity of the earth, as above found, may be applied, it 
is not my bufinefs here to fhew. I fhall therefore put an 
end to this paper with a reflection or two on the premifes 
before delivered. Sir Isaac newton thought it proba- 
ble, that the mean denfity of the earth might be five or 
fix times as great as the denfity of water;, and we have 
now found, by experiment, that it is very little lefs than 
what he had thought it to be: fo muchjuftnefs was even 
in the furmifes of this wonderful man ! Since then the 
mean denfity of the whole earth is about double that of 
the general matter near the furface, and within our 
reach, it follows, that there muft be fomewhere within 
the earth, towards the more central parts, great quantities 
of metals, or fuch like denfe matter, to counterbalance 
the lighter materials, and produce fuch a confiderable 
mean denfity. If we fuppofe, for inftance, the denfity of; 
metal to be 1 o, which is about a mean among the vari- 
ous kinds of it, the denfity of water being 1, it would, 
require fixteen parts out of tvyenty-feven, or a little more 
than one-half of the matter in the whole earth, to be 
metal of this denfity, in order to compofe a mafs of fuch 
mean denfity as we have found the earth to poflefs by 
our 
1 
