ON LIGHT AND COLOURS. 141 



artificial means) has properties other than those which it 

 possesses after it has been some time produced. This will 

 form the subject of a future inquiry. I would suggest, how- 

 ever, at present that the electric fluid ought to be examined 

 with a view to find whether or not it has any property ana- 

 logous to disposition, that is, whether it becomes more 

 difficultly attracted at some distance from its evolution, as 

 light is more difficultly bent at a distance from the point of its 

 being disposed. On heat a like experiment may be made. 

 The thermometer would no doubt stand at a different height at 

 different distances from the source of the heat ; but the ques- 

 tion is if it will not reach its full height, whatever that may 

 be, more quickly near its source than far from it. This 

 experiment ought above all to be made on radiant heat, in 

 which I confidently expect a property will be found similar 

 to the disposition of light. It is also plain that we may 

 expect strong analogies in magnetism and electro-magnetism. 

 I throw out these things because my time for such inves- 

 tigations may not be sufficiently extended to let me under- 

 take them with success. 



PROPOSITION VI. 



The figures made by the inflexion of the second body 

 acting upon the rays deflected by the first, must, according to 

 the calculus applied to the case, be broader than those made 

 by the second body deflecting those rays inflected by the 

 first. 



In fig. 14, let Av' be the violet rays and Ar' the red, 

 inflected by A and deflected by 

 B. Let A?- be the red and 

 A.V the violet deflected by A 

 ind inflected by B. The action 

 f B must inflect Ar, Av into 



broader fringe F, than the 

 iction of B deflects A v', A r' into the fringe /. 



Let B r = a be the distance at which B acts on A r ; rv = d 

 >Q the divergence of the red and violet ; c be the distance of 



