288 SIXTH REPORT — 1836. 



A Paper tva^ communicated entitled Observations for deter- 

 mining the refractive Indices for the Standard Rays of the 

 Solar Spectrum in various media. By the Rev. Baden 

 Powell, M.A., F.R.S., Savilian Professor of Geometry 

 in the University of Oxford. 



This paper contained the details of the observations in a ta- 

 bular form, printed copies of which were distributed. The 

 author prefaced them by a brief statement of the circmnstances 

 which had led to them, and of their nature. The determination 

 of the refractive indices for definite rays of the solar spectrum 

 marked by the dark lines, from the direct observations of their 

 deviations produced by prisms of different substances, first pro- 

 posed and executed by Fraunhofer, for ten media solid and liquid, 

 was carried on by M. Rudberg for ten more cases. The neces- 

 sity for an extended series of such determinations was pointed 

 out and strongly insisted on by Sir J. Herschel, as well as by 

 Sir D. Brewster ; and was further urged by a special recom- 

 mendation from the British Association. [Third Report, p. 

 319.) Not being able to learn that anything has been done 

 towards supplying the deficiency in other quarters, the author 

 took up the inquiry; and the tabular statements contain the 

 results of observations, in which he has attempted to ascertain 

 the refractive indices belonging to each of the standard primary 

 rays for various media : comprising in the present instance the 

 only highly dispersive substances he has been as yet able to pro- 

 cure in a condition capable of prismatic observation ; together 

 with some other liquids of different natures : this being a first 

 contribution only towards a series of such determinations, which 

 he hopes to continue. 



