362 Past Changes in the Universe. [July, 
conclusion following on the recognition of the limited range 
to gravity required by the physical theory. 
Since an explanation of the mechanism of gravity is 
attracting attention at the present time, Le Sage’s theory 
(or a modified form of it) being apparently the only con- 
ceivable one that can satisfy the various conditions of the 
problem, it therefore behoves us to inquire — as a point of 
great interest, and for the furtherance of scientific truth — 
what modification the acceptance of this explanation of the 
mechanism of gravitation (and the important connected 
inference that its range is limited) would make in the views 
as to the operation of physical causation in the Universe ; 
and this inquiry would appear to be all the more desirable 
in view of the accepted faCt that gravitation is really the 
most important physical agency in the Universe, and there- 
fore any modified views regarding its nature and range of 
aCtion would naturally entail important deductions and 
modified views in regard to the working of natural phe- 
nomena. 
The second fundamental conclusion that follows by the 
recognition that the range of gravity is limited , and is 
within the stellar distances, is that the stars must be moving 
in straight lines , and not in orbits, as supposed on the 
assumption of an indefinite range to gravity. It follows 
therefore, by the ordinary laws of probabilities, that if a 
star continue to move in a straight line for a sufficient time 
it must inevitably come into collision with another star situ- 
ated somewhere in the line of the star’s proper motion ; or 
that, in general, collisions among the stars (in a state of 
proper motion among each other in straight lines) must be 
inevitable. This, therefore, may be regarded as the third 
fundamental conclusion that follows by the recognition of a 
limited range to gravity. In the “ Quarterly Journal of 
Science ” for July, 1877,* is a paper by Mr. James Croll, in 
which he calls attention to the fa Cl that some explanation 
is required in order to bring the age of the sun’s heat up to 
the length of time required by the teaching of the faCts of 
geology, and has suggested the collision of matter (in a 
state of proper motion) for that purpose. The mere ap- 
proach of the matter forming the sun under the aCtion of 
gravity without a collision (due to a previously existing 
proper motion) appears to be demonstrably insufficient to 
account for the age of the sun’s heat. It is therefore so far 
satisfactory to observe that the inference of the collision of 
