Cti the Proper tie: of Light, , r , 



VIII. 



Experhiitnls and Ohfervations on the Infexwi, RJlexio/!, and Colours of Light. 

 By Henry Brougham, Jiiii. Efq* 



It has always appeared wonderful to me, fince nature feeras to delight in thofe clofe 

 analogies which enable her to preferve fimplicity, and even uniformity in variety, that there 

 fliould be no difpofitions in the parts of light with refped to inflexion and reflexion ana- 

 logous or fimilar to their different refrangibility. In order to afcertain the. exiftence- of 

 fuch properties, I began a courfe of Experiments and Obfcrvations, a (hort account of 

 which forms the fubftance of this paper. For the fake of perfpicuity I fliall begin wicli 

 the analytical branch of the fubjeft, comprehending my ohfervations under two parts : 



• flexion, or the bending of the rays in their pail'age by bodies, and reflexion. And I fliall 

 . conclude by applying the principles there efl:abli(hed to the explanation of phenomena, ia 

 jthe way of fynthefis. 



, As in every experimental enquiry much depends on the attention paid to the minuted 

 .circumaances, in juftice to myfelf I ought to mention that each experiment was fet down 

 as particularly as poffible, immediately after it was made ; that they were all repeated 



• every favourable day for nearly a year, and before various perfons ; and as any thing like a 

 ^preconceived opinion with refpeft to matter of theory that is in difpnte, will, it is more 



than probable, influence us in the manner of drawing our conclufions, and even in tho 

 manner of recording the experiments that lead to thefe, I have endeavoured, as much as 

 poffible, to keep in view the faying of the Brahmin, " that he who obftinately adheres to- 

 ." any fet of opinions, may bring himfelf at laft to believe that the frefli f»ndal--wood is a. 

 flan)e,of fire*." 



,., i Part I. Of Flexion. 



IN order to fix our ideas on a fubjed which has never been treated of with mathematical 

 preciGon, we fliall fuppofe, for the prefent, that all the parts of light are equally aacd. 

 upon in their pafl;ige by bodies, and deduce feveral of tlie nioft important propofitions 

 which occur, without mentioning the demonfl;rations. 



iDef,. 1.. , If .0: ray pafles within aicertain diftance of any body, it is bent inwards; this wc 

 fliall call inflexion. 2. If it pafles at a.ftill greater diflance, it is turned away ; this may be 

 termed deflexion. 3. The angle of inflexion is that which the inflcded ray makes with . 

 the line drawn parallel to the edge of the inflefting body; and tjic angle of incidence is that 

 made by the ray before inflexion, at the point where it ,_jpcets the parallel. And fo of the 

 angle of deflexion. ' .. . • |. 



Prof of lion I. The force by.whicIi,bodle8,inflej(£i and deflcill the rays, ads in lines per- 

 , pendicular to their furfaces. '.■■;/ 



Prop. 11. The fines of inflexion ^nd deflexion are each of them to the fine of incidence 

 in a given ratio — (and what this ratio is, we fliall afterwards flicw). 



Prop. III. The bending force is to the propelling force of light as the fine of the dif- 

 ference between the angles ,of inflexion (or deflexion and incidence to the cofine of the 

 angle of inflexion or deflexion). 



• Philffcpliici.! Tranfaftions, M.DCcxcvi. i. t 'u'litic Rcfcarchcs, vol. i. p. .*24. 



7 Pr.p. 



