- 
J. Lawrence Smith on Meteorites. 337 
In viewing the cosmical bodies of our system with relation to 
their densities, they are divided into two great classes—planetary 
and cometary bodies (these last embracing comets proper and 
shooting stars), the former being of dense, and the lagter of very 
attenuated matter ; and so far as our knowledge extends, there is 
no reason to believe that the density of any comet approaches that 
of any of the planets: this fact gives some grounds for connect- 
ing meteorites with the planets. Among ‘the planets there is 
also a difference, and a very marked one, in their respective den- 
sities; Saturn having a density of 0-77 to 0-75, water being 1-0; 
Jupiter 2:00-2:25; Mars 3:-5—4:1; Venus 4:8-5-4; Mercury 
tween 7 and 36; Uranus 0-8-2-9 ; that of the Earth being 5-67.* 
If then from specific gravity we are to connect meteorites to 
the planets, as their mean density is usually considered about 
30,t they must come within the planetary range of Mars, Earth 
and Venus. In the cases of the first and last we can trace no 
connection, from our ignorance of their nature and of the causes 
that could have detached them. y 
This reduces us then to our own planet consisting of two parts, 
the planet proper with a density of 5-76, and the moon with a 
density of about 3°62.t On viewing this, we are at once struck 
with the relation that these bear to the density of meteorites, a 
relation that even the planets do not bear to eac r. 
_ As before remarked, I lay no great weight on this view of th 
density, but call attention to it as agreeing with conclusions ar- 
rived at on other ground ews : : 
The chemical composition is also another strong ground in fa- 
Vor of their lunar origin. ‘This has been so ably insisted on by 
Berzelius and others that it would be superfluous to attempt to 
argue the matter any further hete; but I will simply make a 
comment on the disregard that astronomers usually have for this 
argument. Inthe memoir on the periodic meteors by Sears C. 
Walker, already quoted from, it is stated, “ The chemical objec- 
tion is not very weighty, for we may as well suppose a uniform- 
ity of constituents in cosmical as in lunar substances.” From 
is conclusion it is reasonable to dissent, for as yet we are ac- 
quainted with the materials of but two bodies, those of the earth 
and those of meteorites, and their very dissimilarity of consti- 
* ie thane estimates of the densities of the Planets, the author is indebted to 
eirce, 
__ + Although the ave specific gravity of the metallic and ‘stony meteor- 
ites is greater, yet the Anite vaseline the former in quantity, the number 3°0 is 
* 
sity of 30. os 
_--Stooyn Sates, Vol. XIX, No. 87—May, 1855. a 
4 
* 
