noliirnaH bra vtiA jnoa^io***! : tfJto*! .iM 08S 



Mr. Potter's Reply to Professors Airy and Hamilton. 281 



jpterference, proposed by Professor Hamilton, the effects 

 which would arise, according to the formulae he has given, 

 are much too small, and would show that I was perfectly right 

 in considering the irregularity arising in pencils of only a few 

 minutes of a degree in breadth from aberrations to be correctly 

 negligible. 



To find the values of the ordinates for the abscissa? of va- 

 lues 45 and 55 inches, we have 



_ ma? __ ma* I 



y ~~ ±x ~~ 4.z a 

 where, taking the numbers of my former paper, we have 



ma % - -004 14-834 



and I = 44*35 nearly. 



Hence for x — 45 inches y = -000000332 



and x = 55 y = '000003651 



and the difference of these is '000003319, or rather more than 

 three millionths of an inch. 



This difference is so small, that I am sure Professor Hamil- 

 ton would never have given me credit for being so minutely 

 acute an observer, if he had had recourse to actual quantities. 

 It is also easy to determine, that in the experiment the ordi- 

 nate y is not zero at the prism, as the formula indicates it 

 should be. Without having an accurate measurement, I ne- 

 vertheless know that the effect under consideration, from what- 

 ever cause it arises, is at least several thousand times the amount 

 of the above calculated difference. 



Whatever velocity be finally ascertained to belong to light 

 in passing through refracting bodies, it is clear that a different 

 view in the theory of emission must be taken from the New- 

 tonian one of refraction. I recolJect, a long time ago, hearing 

 Dr. Dalton express his opinion in private conversation, that 

 it was not the same light which impinged upon the first sur- 

 face of transparent bodies that left the second surface. It is 

 clear that this view would bring refraction to a similar consi- 

 deration with that of undulations. I have frequently considered 

 the consequences which this view would lead to, and must 

 confess that I do not still see it to be entirely unattended with 

 difficulties, though these might most probably vanish on 

 further study; and I have no hesitation in stating my belief that 

 it will be found to accord better with along range of chemical 

 facts than either of the two other theories. 



.^hiupffi 

 •JiJaraahq lo noiteoup arfi lo nodufos odJ oi tosqesi "rfjiw 



Third Series. Vq| 2. No. 10. April 1833. 2 O 



