362 Messrs. H. E. Roscoe and A. Schuster on the [June 11, 



Isaac Lowthian Bell, F.C.S. 

 W. T. Blanford, F.G-.S. 

 Henry Bowman Brady, F.L.S. 

 Thomas Lauder Brunton, M.D., 



Sc.D. 



Prof. W. Kingdon Clifford, M.A. 

 Augustus Wollaston Franks, M.A. 

 Prof. Olaus Henrici, Ph.D. 



John Eliot Howard, F.L.S. 

 Sir Henry Sumner Maine, LL.D. 

 Edmund James Mills, D.Sc. 

 Rev. Stephen Joseph Perry, 



F.E.A.S. 



Henry Wyldbore Eumsey, M.D. 

 Alfred E. C. Selwyn, F.G.S. 

 Charles "William Wilson, Major 



Prescott a. Hewett, F.E.C.S. I E.E. 



Thanks were given to the Scrutators. 



June 11, 1874. 

 JOSEPH DALTON HOOKER, C.B., President, in the Chair. 



Mr. William Thomas Blanford, Dr. Thomas Lauder Brunton, Professor 

 W. Kingdon Clifford, Mr. Prescott G. Hewett, Mr. John Eliot Howard, 

 Dr. Edmund James Mills, the Eev. Stephen Joseph Perry, and Major 

 Charles William Wilson were admitted into the Society. 



The Presents received were laid on the table, and thanks ordered for 

 them. 



The following Papers were read : 



I. "Note on the Absorption-Spectra of Potassium and Sodium 

 at low Temperatures/ 5 By H. E. ROSCOE, F.R.S., and ARTHUR 

 SCHUSTER, Ph.D. Received April 30, 1874. 



In order to obtain the absorption-spectrum afforded by the well-known 

 green-coloured potassium vapour, pieces of the clean dry metal were 

 sealed up in glass tubes filled with hydrogen, and one of these was then 

 placed in front of the slit of a large Steinheil's spectroscope furnished 

 with two prisms having refracting angles of 45 and 60. The magnify- 

 ing-power of the telescope was 40, and was sufficient clearly to separate 

 the D lines with one prism. A continuous spectrum from a lime-light 

 was used, and that portion of a tube containing the bright metallic 

 globule of potassium was gently heated until the green vapour made its 

 appearance. A complicated absorption-spectrum was then seen, a set of 

 bands (a) in the red coming out first ; whilst after a few moments two 

 other groups appeared on either side of the D lines, the group /3 (less 

 refrangible) being not so dark as the group y. These bands are all 

 shaded off towards the red, and in general appearance resemble those of 

 the iodine-spectrum. In order to assure ourselves that the bands are not 

 caused by the presence of a trace of an oxide, tubes were prepared in 





