418 Professor Airy on the Phenomena 



vibrations are perpendicular to the plane of polarization, I shall 

 say nothing, because I do not think it will be doubted by any 

 one who is well acquainted with the experiments and has ex- 

 amined their agreement with calculation. But on the theorems 

 for intensity in reflected rays, &c, involving points of the 

 greatest obscurity, and supported only by very forced suppositions, 

 any one may I think with reason be sceptical. The phaenomena 

 described here and those described in a former paper (On a 

 remarkable modification, &c.) depend entirely, in theory, upon 

 the changes of sign of certain quantities which enter into 

 FresnePs expressions for these intensities. With respect to the 

 absolute measure of the intensities I can say nothing, except 

 that the general appearance of the brightness is sufficiently in 

 accordance with the law. On the whole I think that these 

 experiments give great probability to the truth of the formula 

 considered as a general law : and that they establish with 

 certainty that part of it which implies that, after passing a 

 certain angle, the direction of the vibration in the reflected 

 ray (considered with respect to that in the incident ray) is 

 reversed. 



Observatory, G. B. AIRY. 



Feb. i, 1832. 



POSTSCRIPT. 



Since the above account was written I have (with a favour- 

 able sky) seen the white-centered rings many times, and several 

 times with a doubly-refracting prism only, unassisted by a 

 tourmaline. In examining one part of the phenomena I find 

 that there is a discordance of a most curious kind from what 

 the strict theory had led me to expect. 



