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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



gravitation which has yet withstood the test of 

 criticism, viz., that of Le Sage, 1 and which has 

 been received with some favor by some of the 

 most eminent physicists, it is certain that the 

 range of gravity cannot extend to indefinite dis- 

 tances. It is therefore quite possible that the 

 range of gravity may not extend to the stellar 

 distances so that the stars do not gravitate tow- 

 ard each other. 4 This would evidently be the 

 condition required to satisfy the very important 

 point of stability in the universe. The range 

 through which gravity has been actually ob- 

 served to prevail is known to be infinitesimal 

 compared with the stellar distances, so that the 

 range of gravity may perfectly well lie within 

 these limits. Thus the condition for stability is 

 the first important conclusion following on the 

 recognition of the limited range to gravity re- 

 quired 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 conceivable one that 

 can satisfy the various conditions of the prob- 

 lem, it therefore behooves us to inquire — as a 

 point of great interest, and for the furtherance 

 of scientific truth — what modification the ac- 

 ceptance of this explanation of the mechanism 

 of gravitation (and the important connected in- 

 ference that its range is limited) would make in 

 the views as to the operation of physical causa- 

 tion in the universe ; and this inquiry would ap- 

 pear 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 

 therefore any modified views regarding its nature 

 and range of action would naturally entail im- 

 portant deductions and modified views in regard 

 to the working of natural phenomena. 



The second fundamental conclusion that fol- 

 lows 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 as- 



1 In three papers published in the Philosophical 

 Magazine (September and November, 1877, and Feb- 

 ruary, 1878) it has been my object to show how Le 

 Sage's original theory may be modified, and certain 

 difficulties in the way of its acceptance (in its origi- 

 nal form) removed by the light of the modern investi- 

 gations connected with the kinetic theory of gases. 

 A fourth paper, after the MS. of the present paper was 

 written, has also been published in the Philosophical 

 Magazine for April last. 



2 Of course we do not allude to double stars, in 

 close range. 



sumption of an indefinite range to gravity. It fol- 

 lows, therefore, by the ordinary laws of probabili- 

 ties, that if a star continue to move in a straight 

 line for a sufficient time, it must inevitably come 

 into collision with another star situated some- 

 where 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, there- 

 fore, may be regarded as the third fundamental 

 conclusion that follows by the recognition of a 

 limited rangf to gravity. In the Quarterly Jour- 

 nal of Science for July, IS 1 ?*?, 1 is a paper by Mr. 

 James Croll, in which he calls attention to the 

 fact 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 approach of the matter 

 forming the sun under the action of gravity with- 

 out a collision (due to a previously-existing 

 proper motion) appears to be demonstrably in- 

 sufficient 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 masses (in a 

 state of proper motion), arrived at on indepen- 

 dent grounds by Mr. Croll, is precisely the same 

 conclusion that necessarily follows from the de- 

 duction that the range of gravity is limited, and 

 therefore that the stars necessarily move among 

 each other in straight lines, whereby, in the nat- 

 ural course of things, collisions are rendered in- 

 evitable. The eventuality of collisions among 

 the stars is also treated of in a paper by Mr. 

 Johnstone Stoney, " On the Physical Constitution 

 of the Sun and Stars " (" Proceedings of the Roy- 

 al Society," 1868-'69). 



The question of difficulty that remains would 

 be to explain bow the colliding matter of the uni- 

 verse is separated and prevented from aggregat- 

 ing together to an indefinite extent. The limit 

 to the range of gravity and the limit to the inten- 

 sity of gravity required by the physical theory 

 would appear to have a bearing here. It may be 

 observed that there are two opposing agencies, 

 the expansive action of heat and the contractive 

 action of gravity. By the continued aggregation 

 of matter the expansive action of heat increases, 

 while the intensity of the contractive action of 

 gravity attains a final limit. It would, therefore, 

 appear reasonable to conclude that a balance 

 would naturally set in, at which the expansive 

 action of heat would compensate the contractive 

 1 Also Philosophical Magazine, 1868. 



