Proceedings of the British Association. 115 



of England was still greater than had been stated by the Bishop 

 of Norwich. If his memory did not deceive him — while in London 

 the annual depth was only 23 inches, in Keswick it was no less than 

 60. — Mr. Roberts observed, that the discrepancies in the registries 

 of rain-gauges were such as to render great caution necessary in 

 drawing conclusions. It was now beginning to be understood that 

 unless the rain-gauges were placed on a level with the earth, no 

 indication would be obtained from them of the quantity which fell on 

 the surface. — The Astronomer Royal said that there was something 

 still unexplained as to the effect of the altitude at which the rain- 

 gauge was placed, on the amount of rain received ; while the quantity 

 of rain received in the gauge on the top of the Observatory was less 

 than that placed in the court below, yet a guage placed at the foot of 

 Greenwich Hill, which was at a considerably lower level than either, 

 received less rain. — Sir J. Herschel believed that the cold drop as 

 it descended from above, received accessions from the vapour of the 

 air through which it passed ; and if this be the true account, then 

 the explanation was complicated by the relative hygrometric states and 

 temperatures of the several strata of air. 



' On certain points in the Elliptic Polarization of Light, by re- 

 flexion from metallic surfaces/ by Prof. Powell. The object of 

 this communication was supplementary to one given last year ; since 

 which time the author has extended his researches to some of the re- 

 lations of the subject not before adverted to. The original plane of 

 polarization being inclined 45° to that of incidence on metal in the 

 lower degrees of ellipticity, i. e. at smaller incidences, the dislocated 

 rings preserve the distinction of the dark and bright systems, which 

 they lose, when the vibrations are absolutely circular; also at the 

 position of the analyzer, intermediate to the rectangular positions, the 

 coloured arcs assume a peculiar distorted appearance. A generaliza- 

 tion of the formula, employed in the author's paper [Phil. Trans. 

 1843], so as to include all positions of the polarizer and analyzer, 

 and assuming the component vibrations with general, or unequal, co- 

 efficients, — is necessary for explaining the last-mentioned pheno- 

 menon ; while the former supplies the best means of directly observ- 

 ing the change in the virtual plane of polarization of the reflected 

 ray, by means of the position necessary to be given to the analyzer, 



