PROCEEDINGS 



OF THE 



Camkifcrg* Ifi^ibsnp^iral Sbrktg, 



On the variation ivith the wave-length of the double refraction 

 in strained glass. (Third paper.) By L. N. G. FlLON, B.A., 

 King's College. 



[Received 23 December 1903.] 



1. The investigations which form the subject of the present 

 paper are a continuation of those described in my previous paper 

 (Camb. Phil. Soc. Proceedings, Vol. xil. Part i. pp. 55 — 64). The 

 apparatus employed was precisely the same and need not there- 

 fore be again described. 



The glasses experimented upon were a series of glasses manu- 

 factured by Messrs Zeiss of Jena. They were selected as follows. 

 The refractive index and mean dispersion were plotted to density 

 from the numbers given in Zeiss's catalogue. A series of glasses 

 were then taken, for which both refractive index and mean dis- 

 persion appeared to vary regularly with the density. The glasses 

 thus selected were found from the same catalogue to be silicate 

 flints. 



Seven glasses in all were chosen, bearing the Jena catalogue 

 numbers O 152, O 154, O 103, O 192, O 41, O 198, S 57. Blocks 

 of dimensions 1 cm. x 4 cms. x 3 cms. were made for me by Messrs 

 Zeiss, the faces 1x4 being polished. A rough description of the 

 composition of each glass, and the approximate percentage of 

 PbO were communicated to me through the courtesy of Messrs 

 Zeiss to whom my obligations are due. The descriptions of the 

 glasses, i.e. density, refractive index, mean dispersion and general 

 chemical composition, are given in Table I. below. 



VOL. XII. pt. v. 21 



