Messrs. Clayden and Heycock on the Spectra of Indium. 387 



both angles. The real symbol is also to be found for the dis- 

 turbed face a ; reduced to the system of the enstatite, it has 

 the symbol (a : §6 : e), P§. For the inclination of this face 

 we have 



m! : <r = 124° 16 / j %'• o-=15i° ll 7 . 

 We must compare these angles with the above in order to re- 

 cognize the degree of perturbation. There are yet several 

 other faces on the enstatite crystals from Kjorrestad, the 

 symbols of which, in consequence of their imperfections, cannot 

 be definitely determined. Such faces are not indicated by a 

 letter in our figure. This richness of faces recalls to mind the 

 meteoric enstatite of the Breitenbaeh iron, which were deter- 

 mined by von Lang's sagacity. The cause of the remarkable 

 monoclinic formation of the Norwegian enstatite is quite 

 hidden. The first thought may be that it is the result of pres- 

 sure. But that explanation must be surrendered if we ob- 

 serve that the monoclinic dislocation is only to be seen in the 

 faces of the summit, and never in the vertical faces. So this 

 anomaly seems to have its origin in crystallonomic causes. 

 The exhausted apatite-mine of Kjorrestad is hitherto the only 

 known locality of these enstatite giants. No doubt implanted 

 enstatite crystals will be found in other plutonic localities. 

 If we shall there be able to observe the crystals not merely 

 among the materials thrown away, but also in their natural 

 position in situ, we may possibly find a solution for the dislo- 

 cation of the terminating faces, which is at present an enigma. 

 Bonn, October 4, 1876. 



XLVII. The Spectra of Indium. By Arthub W. Clayden, 

 B.A., and, Charles T. Heycocx*. 



SOME time ago, while working at a course of lectures on 

 spectrum-analysis, given by the Professor of Chemistry, 

 we noticed that the spectrum of indium, as obtained by pass- 

 ing the spark from an induction-coil between points of the 

 metal, differed from that given in the various books on the 

 subject. Instead of the three lines expected, we found sixteen. 



During the past summer we have investigated the matter, 

 with the following results. 



When the spark is used to decompose and volatilize the 

 chloride of the metal, the spectrum ordinarily given in the 

 books, namely two lines in the indigo and one in the violet, is 

 seen. Thalen gives the following measurements for these — 

 4532, 4509, and. 4101; but Ave are inclined to think 4510 is 

 nearer the truth than 4509. 



* Communicated by the Authors. 



2C2 



