Review of Hall and Whitney's Geology of Iowa. 108 
seem to be that. the earth is actually, in a certain sense, a comet, 
and that its luminous train is seen by us in the Zodiacal Light. 
The nebulous earth-ring contended for by the Rey. Mr. Jones, in 
explanation of his admirable observations upon the zodiacal light, 
seem then, in a modified sense, to have a real existence ; 
instead of being in a condition of statical equilibrium, as sup- 
Posed, it is in a dynamical condition of perpetual dispersion and 
_ -Tenewal,* 
that stream out in various directions, and perhaps also the rose 
colored flames that here and there project beyond the dim circular 
n. 
3 Note—It would seem that even the visible nucleus of a comet is not in a truly stat- — 
ab condition, It contracts and enlarges with the varying distance from the sun, This 
e ce, arising from th rying luminosity of the photos 
It is also possible that the inner nucleus, with its rato phere. may be intone 
b ereal atmosphere, which contracts a reason of variations in 
an impulsive action of the sun, and in the density of the ether of space, in the vi- 
. ty s Th arks may also apply to the entire enve pe of | gs 
comet, and th mplete spherival envelopes sometimes noticed, Spherical envel- 
pes entirely surrounding the ucleus, would also etic 
jected from all 0 velocity, but 
be proj . the same velocity, bt 
force Insufficient to overcome the gravitating tendency. An apparent spherical 
Continuation of an envelope behind’the nucleus, might, portene result from the in- 
“ctlons of the orbits of the cometary particles urged past it into space by the re- 
Pulsive force of the sun, 
A more accurate determination of the orbits of the cometic particles will be giv- 
0 iN a succeeding No. of the Journal, 
— 
Ale, SV Reesein of Hall and Whitney’s Report on the Geology 
of Lowa.t 
_ THE first volume of the Report on the Geology of Towa has 
just been published, and in a style highly honorable to the State, 
The State embraces much that is of scientific and practical interest, 
* 
mote should en! 
a Repo on the Geological Survey of the State of Iowa: embracing the results 
Hany tigations made during portions of the years 1855, 56 and 57. By James. 
* State Geologist, and J. D. Wuirney, Chemist and Mineralogist. Published 
Suthority of the Legislature of : Vol. pp. 724, 1868. 
