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LXXVII. Further RemarJcs on Experiments relative to ike 

 Interferevcc of Light. By the Rev. Baden Powell, M.A., 

 F.R.S., Savilian Professor of Geometri/, Oxford*. 



TN a papei' which appeared in the Philosophical Magazine 

 -*■ and Annals, N.S. tor January 1832, I described a few ex- 

 periments, having in view the fuller illustration of the prin- 

 ciple of interferences, and of the undulatory theory of light. 

 Those remarks claim no higher character than that of at- 

 tempts to simplify some points in the inquiry, and facilitate 

 the diffusion of elementary knowledge on this most beautiful 

 and interesting branch of science; and it is with no other ob- 

 ject that the present paper has been drawn up. 



There are, in fact, few parts of science (especially consider- 

 ing the experimental and popular form of which it is suscep- 

 tible,) which have excited less general attention than that to 

 which the name oi physical optics has been applied. And I 

 would observe, in passing, that as the distinction implied in 

 this designation between the properties of interference, polari- 

 zation, &c., and those of ordinary reflexion and refraction is 

 "wholly arbitrary^ — these last being just as much physical pro- 

 perties as the former, — it would surely be better to restrict the 

 term "/.'//j^j/caZ optics" to a sense analogous to '^physical astro- 

 nomy" viz. to the theory of those motions and forces which 

 shall account for the observed effects on dynamical principles. 

 This is quite independent of the facts. Nor is the distinction 

 merely verbal, for I believe that an imagined inseparable con- 

 nexion between the facts of the coloured rings, polarization, 

 &c. and the physical theory, has tended in no small degree to 

 create a reluctance in many persons to enter upon a subject 

 which was supposed to be identified with a doubtful, abstruse, 

 and difficult hypothesis. 



In this point of view, therefore, the distinction may be by no 

 means unimportant. Long since, indeed, those who were most 

 profoundly versed in the subject were not backward in their 

 attempts to dispel such misconceptions. The present Lord 

 Chancellor Brougham, in his highly acute and original papers 

 " On the Reflexion, Inflexion, and Colours of Light," in the 

 Philosophical Transactions for 1 796-97, insisted strenuously 

 on the distinction between the facts of Newton's experiments 

 (which he pursued and extended) and the theories whether of 

 fits or waves ; and though he rejected both for a simpler 

 theory of his own, this was at a period when the real nature 

 of either was as yet undemonstrated. And when the singu- 

 lar fact of interference was unequivocally established by Dr. 

 • Comniunicatnd by the Author. 



Third Series. Vol. I . No. 6. Dec. 1832. 3 K 



