G, Hinrichs on the Density, Rotation, and Age of the Planets. $7 
far as possible, then we must accept a different course of inves- 
tigation, We must do for astronomy what geology has done 
for geography—in the absence of records from the earlier stages 
of the earth’s history it has been successfully attempted to 
supply them by observations on the configuration of the earth’s 
parts, carefully compared with the yet continuing changes 
thereof’ We must try to investigate the different celestial strata, 
try to see whether they are in situ or displaced, and, if displaced, 
measure the force which produced the dislocation: then we will 
obtain as good determinations of the relutive age of these celestial 
strata or planets and moons as geology affords for the relative 
age of terrestrial stratu.2 As far as Induction is to be relied on 
in geology it may safely be relied on in astronomy, and we 
hope to show that the known observed configuration of tbe 
solar system gives, by means of the calculus and a strict induc- 
tion, as good a determination of the relative age and the resisting 
lorces as geology can produce in regard to the earth’s crust. If 
then geology, notwithstanding its yet leaving many questions 
undecided, is considered more than idle speculation, we hope to 
vindicate the same confidence for the results of this investigation 
into the nature and effects of the dislocating force of the solar 
system: we will try to show that the resistance of the ether filling 
different distances, we easily find that the year would be short- 
ened only one second in a thousand years by this resistance! 
this quantity is imperceptible, resistance is; but the latter cannot 
I. The effects of Resestance. 
_ Let r be the radius vector, 6 the anomaly, ¢ the time, 7 the 
angle between the orbit and a perpendicular to the radius vector, 
and R th accelerating force due to the resisting medium; then 
_* See an example in Dana’s Manual of Geology, p. 386, where the relative age 
of the Sil ecaha Canaaae «ths owes i 
