318 Prof. PowelPs Notes on Repulsion by Heat^ S^c, 



order of the scale, and rapid contraction and final disappear- 

 ance of the rings, between lenses or plates of glass. This 

 method 1 showed was at once decisive and simple; the 

 " warping" or change of figure (if any) in the glasses by 

 heat being readily seen to be such as ought to cause the rings 

 to enlarge at the first instant. It seemed to me a method 

 easily applicable to a number of other points of inquiry con- 

 nected with the subject ; and to many such topics I began at 

 that time to turn my attention. 



The subject is evidently one which may have extensive 

 bearings on a variety of points connected with the study of 

 molecidar forces. On these it was once my intention to have 

 entered : but various circumstances have led me to discontinue 

 such researches, more especially the superior attractions pre- 

 sented by the study of physical optics, and the observations 

 and calculations connected with the verification of the theory 

 of dispersion, in which I have been, and am likely to be, en- 

 gaged. This subject at present engrosses all the time and 

 attention I can devote to physical research, more especially 

 in the present stage of its advance : it seems to call for a com- 

 prehensive review and systematic methodizing of the principles 

 of the undulatory theory ; and in attempting something towards 

 the great work of a systematic treatise on the Mechanism 

 OF Light, I am now likely to find ample employment, pro- 

 bably for some years to come. 



Under these circumstances, in looking over and destroying 

 a number of old papers, I thought that perhaps a few rough 

 memoranda of trials of experiments, and flints for others, con- 

 nected with the subject of repulsion by heat, which had been 

 thrown aside formerly in the hope of some day resuming the 

 subject,^ might possibly be not altogether unworthy of pre- 

 servation, if they should only have the effect of drawing the 

 attention of any experimenter to the subject, and inducing him 

 to pursue it. With this object I thought the best course would 

 be to request your insertion of the few following notes of this 

 kind in your Journal ; trusting that your readers will look 

 upon them in no other light than as suggestions of experi- 

 ments rather than as definite experimental investigations. 



(1.) Most of these experiments were performed by forming 

 the rings simply between two plates of glass and not with 

 lenses. It is very easy in this way to obtain rings of tolerably 

 regular form. The warping of the glasses by the heat has 

 been alleged as likely to interfere with the results; but I have 

 observed above (as indeed a very little consideration will suf- 

 ficiently evince) that this cannot produce any effect. But 

 further, according to the experiments of Sir David Brewster 



