ON LIGHT. 



same kind as that afforded of the intrinsic tensile strength 

 of a wire or thread of any material by the statement of 

 how much in length of 'itself 'it can bear without break- 

 ing. It frees us from the necessity of any mental refer- 

 ence to the actual weight or specific gravity of the 

 material, which in this case is the more necessary, as, 

 though we suppose the ethereal molecules to possess 

 inertia, we cannot suppose them affected by the force of 

 gravitation. 



(67.) There is yet another theory of light which might 

 be proposed, in which, still retaining the idea of an 

 ethereal medium, its constitution should be conceived 

 as an indefinite number of regularly arranged equidistant 

 points (mathematical localities) absolutely fixed and im- 

 movable in space, upon which, as on central pivots, the 

 molecules of the ether, supposed polar in their constitu- 

 tion, like little magnets (but each with three pairs of poles, 

 at the extremities of three axes at right angles to each 

 other), should be capable of oscillating freely, as a com- 

 pass-needle on its centre, but in all directions. Any one 

 who will be at the trouble of arranging half a dozen 

 small magnetic bars on pivots in the linear arrangement 

 of the annexed figure, will at once perceive how any 





Fig. 5- 



vibratory movement given to one, at any point of the 

 chain, will run on, wave-fashion, both ways through its 

 whole length. And he will not fail to notice that the 



