88 Prof. Brlicke on Gravitation and 



spaces between these masses being traversed by the forces. If 

 the forces could be imagined as existing in spaccj it must also be 

 conceivable that matter may be annihilated without changing the 

 sum of the forces, and this, at least by me, is not conceivable. 



One more point remains to be considered, which I believe is 

 essential to the doubts i-aised by Taraday. We say the attrac- 

 tion diminishes with increasing distance, and moreover that the 

 attracting forces are to each other in the ratio of the inverse 

 squares of the distances. In Faraday's process of thought, this 

 is understood as if we assumed a change of the cause of motion 

 which actually resides in the masses. I do not know whether 

 this is a pi-evalent notion. It is difficult to obtain information 

 on the point, for an investigator may write memoirs all his life 

 long and never once express his convictions upon the subject. 

 I believe, however, it cannot be doubted that Faraday is right in 

 opposing this notion, and in assuming with Newton the existence 

 of a constantly active cause for g';avitation. I believe also it may 

 be shown that this assumption of Faraday's contradicts neither 

 the facts themselves, nor the usual mode of interpreting them. 



We say that the attracting forces vary inversely as the squares 

 of the distances ; we also say that the intensity of light varies 

 inversely as the squares of the distances, but are thereby far from 

 affirming anything regarding the intensity of the source of light 

 itself. We speak solely of the effects upon surfaces exposed to 

 the radiation, and know very well that the intensity of the lumi- 

 nous source will not be in the least affected by the proximity or 

 the distance of the illuminated objects. When the rays of light 

 were regarded not only as mathematical lines, but as the paths 

 of the light parlicles, it was said the intensity of the light dimi- 

 nishes inversely as the squares of the distances, because the areas 

 on which an equal number of rays fall, augment directly as the 

 squares of the distances. Now that we deduce the action of 

 light from wave-motions, we know that the intensity must obey 

 the law of inverse squares, because during the propagation the 

 same sum of vis viva is incessantly transferred to new masses, 

 which augment directly as the squares of the distances. The 

 change as the inverse square of the distance, appears to us now 

 as a simple application of the law of the conservation of force. 



We regard the attractive force residing in a mass as proceed- 

 ing in straight lines from it in all directions, just as light sends 

 its rays on all sides ; and as we perceive the light when the 

 retina, or a body seen by us, falls in the domain of the rays, so 

 in like manner we perceive the action of the attractive forces 

 when a body comes in their Vt'ay *. When, therefore, we say, the 



* The raj's of I'glit exist independent of the presence of the second body, 

 but is this ihe case with force ? Docs not the conception of force carry with 

 it that of two material masses at least? If so, when one mass vauisbes, 

 force becomes a nonentity. — Ed. 



