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III. On Photometry in connexion mth Physical Optics. 

 By R. Potter, Esq., B.A., F.C.P.S., Medical Fellow of 

 Queen'' s College, Cambridge^'. 



THAT Photometry should have excited some attention 

 amongst scientific men, could scarcely fail of proving a 

 cause of satisfaction to the writer of the present paper, who 

 had several years ago urged its great importance in laying an 

 experimentiil foundation in Physical Optics. If the subject 

 had been approached in a philosophical spirit, with a real de-- 

 sire to find out the truth according to the principles laid down 

 by Lord Bacon, that satisfaction must have been the writer's 

 privilege. Very different however has been the notice it has 

 called forth. 



The dazzling fruits of Fresnel's genius had so blinded the 

 scientific world, that it has been held to be presumption to 

 examine minutely the accuracy of his results, although his 

 constitution of mind must have indicated the need of this, to 

 the most cursory reader of his various papers. We there see 

 the zeal of the advocate to carry his point, overruling his 

 judgement, and leading him to make objections against the 

 theory he opposed, which were frequently either incorrect in 

 their foundation, or were of trivial importance. 



It matters little to say such and such things are in them- 

 selves improbable or unintelligible; for if the theory give re- 

 sults in accordance with natural phaenomena, we are bound to 

 receive it, although many of its consequences should seem 

 strange and even inadmissible at the first view: thus, I con- 

 ceive, no one would be justified in rejecting the undulatory 

 theory of light, or any other, if its results were in accordance 

 with experiments. 



The fashion of pinning their faith on Fresnel's sleeve having 

 become general amongst the influential in learned societies, 

 and amongst the most eminent in mathematical attainments, 

 it was natural that minds of smaller calibre, or reputations of 

 smaller weight, should feel it a readier and surer way to ho- 

 nours and distinction to follow in the tide, without venturing 

 to dispute the judgement of their superiors or to question their 

 infallibility. Under such circumstances the mere analyst must 

 find himself floating in the tide with those who claimed a more 

 profound knowledge of experimental philosophy, and who 

 vi^ere sure to applaud the aid he rendered to the common 

 cause in symbols and formulae, of which they were frequently 

 as little able as willing to investigate the accuracy. 



* Communicated by the Author. 



