376 THE CONSERVATION OF FOKCE. 



at a distance, or whether the ether, or some other medium, is 

 not necessarily present. 



"We are not permitted as yet to see the nature of the source 

 of physical power, but we are allowed to see much of the 

 consistency existing amongst the various forms in which it is 

 presented to us. Thus, if, in static electricity, we consider 

 an act of induction, we can perceive the consistency of all 

 other like acts of induction with it. If we then take an elec- 

 tric current, and compare it with this inductive effect, we see 

 their relation and consistency. In the same manner we have 

 arrived at a knowledge of the consistency of magnetism with 

 electricity, and also of chemical action and of heat with all 

 the former ; and if we see not the consistency between gravi- 

 tation with any of these forms of force, I am strongly of the 

 mind that it is because of our ignorance only. How imper- 

 fect would our idea of an electric current now be, if we were 

 to leave out of sight its origin, its static and dynamic induc- 

 tion, its magnetic influence, its chemical and heating effects ; 

 or our idea of any one of these results, if we left any of the 

 others unregarded ? That there should be a power of gravita- 

 tion existing by itself, having no relation to the other natural 

 powers, and no respect to the law of the conservation of force, 

 is as little likely as that there should be a principle of levity 

 as well as of gravity. Gravity may be only the residual part 

 of the other forces of nature, as Mositi has tried to show ; 

 but that it should fall out from the law of all other force, and 

 should be outside the reach either of further experiment or 

 philosophical conclusions, is not probable. So we must strive 

 to learn more of this outstanding power, and endeavour to 

 avoid any definition of it which is incompatible with the prin- 

 ciples of force generally, for all the phenomena of nature lead 

 us to believe that the great and governing law is one. I 

 would much rather incline to believe that bodies affecting 

 each other by gravitation act by lines of force of definite 

 amount (somewhat in the manner of magnetic or electric in~ 



