i88i.] 
Some Results of Gravitation . 
705 
result of such a process. One of its effects would be to 
diminish the rapidity of internal compression, so that the 
surface region may have become greatly condensed, or even 
solidified, to a considerable depth, while the reduction of 
gravity and the resistance of temperature kept the interior 
substance in the state of a rare gas. But as the superficial 
region grew denser the centrifugal gravity of the portion of 
gas adjoining it internally must have augmented, until in 
time it may have equalled the centripetal gravity. We 
would have the case, in faCt, of a mass of matter in contact, 
on one side, with a thick region of dense matter strongly 
attracting it upwardly; and, on the other side, with a much 
thicker region of rare matter, attracting it downwardly with 
comparative weakness. And this rare region would be com- 
plemented, at a very considerable distance, with a dense 
region equal in thickness to the first, but so much more dis- 
tant as to greatly reduce its attractive effect upon the mass 
of matter in question. 
In consequence, it is not difficult to conceive of a process 
of terrestrial evolution somewhat as follows : — Compression 
of the nebula necessarily first took place at the surface. As 
it extended inwardly the heat set free hindered its rapid ex- 
tension. The attraction of this dense surface region upon 
the interior gas reduced the centripetal gravity of the latter, 
and possibly, at length, completely negatived it. It may, 
indeed, have gone further than this. It may have reversed 
the gravity of the matter adjoining the inner surface of 
the dense surface shell. Instead of gravitating down- 
wards, the matter in this region may have commenced 
to gravitate upwards, the effective attraction of the adjacent 
dense matter overbalancing that of the interior rare matter 
and the distant dense matter of the opposite surface. 
In such a not inconceivable condition of things there 
would be a most effective hindrance to the inward extension 
of density. This, at first hindered by the resistance of tem- 
perature, became also hindered by a growing reduction of 
the downward gravity of the interior substance. Eventually 
this downward gravity may have become first negatived, and 
then reversed, it being replaced by an upward gravity. 
Going downward from the surface we would first pass 
through a region of downward pressure. At a certain depth 
this would reach its limit of effectiveness, the extra weight 
produced by increased density being balanced by the reverse 
effeCt of upward attraction. Going still deeper, the effeCt of 
this upward attraction must augment, and the downward 
gravity decrease. This decrease must regularly continue 
