[Kirkwood 
Oct. 6. 1871.] 163 
On the Formation and Primitive Structure of the Solar System. 
By Proressor DANIEL KIRKWoOD. 
(Read before the American Philosophical Society, Oct. 6, 1871.) 
The development of any branch of science is generally a slow and 
gradual process, The obvious truths which suggested to Laplace his cele- 
brated hypothesis of the solar system had been for ages well known to 
astronomers ; but, as in the case of the earlier geological observations, 
they had been regarded, without any just reason, as ultimate facts. So 
now we have numerous results of observation in regard to the rings of 
Saturn, the zone of asteroids, the relative distances of the planets, &c., 
the study of which, it is believed, may lead to new and important discov- 
eries. ‘These hieroglyphics older than the Nile,”’ pointing back to the 
epochs at which the planets were born, will doubtless in the future be 
more or less clearly deciphered, and the ancient history of the solar system 
at least partially developed. 
It is a very remarkable fact in regard to the systems of both primary 
and secondary planets that the periods, without any exception, have very 
simple relations of approximate commensurability. This truth, though 
obvious on mere inspection, seems not to have attracted the special notice 
of astronomers, as no attempt had been made, previous to that of the 
writer, to assign its physical cause. A general view of these approxima- 
tions is presented in the following tables, where the periods of the primary 
planets, Mercury, Venus, &e., are represented by P!, P1?, &e., and those 
of the satellites by p', p!?, &c. 
I: 
Tur PRIMARY SYSTEM. 
VIII VIL < 
yp TIT __89.37 years==P —1.65y. 
ype opi 6 Pa, -14> 
peer si, P0008 
ph 97 <P +000 
pe ckorages vere: 0012 
ppl 20.667 << =P: 40.052 
2p 0,246 “| =P* —0.005 
TI. 
Tur JovIAN SYSTEM. 
aply ee ognhg <8 
in pe +36 40 
Lp 9 45 
a 
