Royal Society, 309 



moreland, described in a former paper, and those drawn from the 

 same facts by Mr. Homersham, in a paper read before the Society 

 on the 25th of May last, states that the results for the year 1848 

 show a precisely similar gradation to those of the two preceding 

 years ; and that the whole of the observations appear to warrant the 

 conclusion which he had ventured to draw from those detailed in 

 his former paper. 



He remarks that, as the rain-gauges are, with one exception, si- 

 tuated on the high mountains surrounding tiie head of the Vale of 

 Wastdale, this valley is the only one which can fairly be selected as 

 a standard in comparing the quantities of rain obtained at the differ- 

 ent mountain stations. The discordance between his conclusions and 

 those arrived at by Mr. Homersham, he considers, has arisen from 

 that gentleman having selected the distant and excessively wet loca- 

 lity of Seathwaite at the head of the southern fork of Borrowdale, 

 as a representative of the quantity of water deposited in the valleys 

 generally. 



If the receipts of the mountain gauges, he observes, be compared 

 with the rain-fall at Wastdale Head, or in any of the other valleys 

 except Seathwaite, it will be found that the quantity increases con- 

 siderably up to 1900 feet, where it reaches a maximum; and that 

 above this elevation it rapidly decreases, until at 2800 feet above the 

 sea the amount is very much less than in the surrounding valleys. 



In conclusion, the author states that it appears to him, that much 

 of the discordance in the resultsobtained atvarious elevations amongst 

 the mountains has arisen from the circumstance of the instruments 

 having been placed on the slope or breast of the hill nearly in a line 

 with each other ; in which positions, he is convinced from experi- 

 ence, that when strong winds prevail, the gauges are exposed to eddies 

 or counter-currents, which prevent a portion of the water from enter- 

 ing the funnel, and thus a less depth of rain is obtained than is due 

 to the elevation. 



The gauges under his superintendence being all stationed either 

 on the top or shoulder of the mountain, and exposed to the wind 

 from every point of the compass, are not, he observes, open to this 

 objection. 



Supplement to a paper " On the Theory of certain Bands seen 

 in the Spectrum." By G. G. Stokes, Esq., M.A., Fellow of Pem- 

 broke College, Cambridge. Communicated by the Rev, Baden Powell, 

 M.A., F.R.S. 



The principal object of the author in this communication is to 

 point out some practical applications of the interference bands re- 

 cently discovered by Professor Powell, the theory of which was con- 

 sidered by the author in the paper to which the present is a supple- 

 ment. The bands seem specially adapted to the determination of 

 the dispersion in media which cannot be procured in sufficient purity 

 to exhibit the fixed lines of the spectrum. The ordinary experi- 

 ments of interference allow of the determination of refractive indices 

 with great precision ; but in attempting to determine in this way the 

 dispersion of the retarding plate employed, there is the want of a 



