REPORTS 



THE STATE OF SCIENCE. 



Report on the present state of our knowledge of Refractive 

 Indices for the Standard Rays of the Solar Spectrum in dif- 

 ferent media. Presented to the British Association for the 

 Advancement of Science. By the Rev. Baden Powell, 

 M.A., F.R.S., F.G.S., F.R.Ast. S., Savilian Professor of 

 Geometry, Oxford. 



[With two Plates.] 



AN submitting to the British Association a Report on this sub- 

 ject, on the present occasion, after having already, from time to 

 time, made various statements relative to such results, both to 

 the Association and in published papers, — it may be necessary 

 to explain, that those former statements embraced only detached 

 portions of the subject, and in many instances contained only 

 first, imperfect, and approximate results, which I was neverthe- 

 less anxious to bring forward at the time, in order to afford 

 some means of attempting comparisons with theory. These 

 results have been since rendered more accurate by further repe- 

 titions, and some points which seemed doubtful, no\v cleared 

 up : though I have still to regret that it has not been in my 

 power, as yet, materially to extend the range of media examined. 

 To state, however, the entire series of such results as I can now 

 with any confidence offer, and to collect in one view all the 

 other determinations of the kind as yet known to have been ob- 

 tained, is the object of the present Report. 



The historical memoranda of these researches may be briefly 

 stated by way of introduction. 



Fraunhofer was beyond question the first who used the dark 

 lines as points of measurement for the deviations of definite 

 primary rays, in seven kinds of glass, and three liquids. His 

 original memoir appears in the Munich Transactions [Benk- 



voL. VIII. 1839. B 



