Intelligence and Miscellaneous Articles. 237 



The sample had the appearance of a large mass of steel-grey 

 crystals, radiating chiefly from a central point ; some of the crystals 

 being fully an inch in length, and generally very perfectly formed. 

 The crystals were prisms belonging to the trimetric system, soft, 

 and easily cut with the knife, in the direction parallel to the prin- 

 cipal axis, showing when cut a brilliant metallic lustre. 



Adhering to the crystals was a small amount of gangue, composed 

 seemingly of siliceous matter. 



For the purpose of analysis, a large crystal was broken off per- 

 fectly free from any foreign matter. The specific gravity of the 

 crystals =4*625. The following are the results of the analysis : — 



Antimony 71*09 



Iron ... 0-24 



Arsenic traces 



Sulphur 2847 



99-80 



ON THE REVERSAL OF THE LINES OF THE SPECTRA OF METALLIC 

 V_4POURS. BY M. A. CORNU. 



In studying the spectrum of the spark of magnesium, which 

 serves me as a monochromatic light for photographing the coloured 

 rings*, I have been led to a series of observations which appear to 

 have some interest in respect of the study of the solar spectrum. 



My purpose was to photograph the line, in the spectrum of the 

 magnesium-spark, which produces by itself alone the greater portion 

 of the photogenic energy. This line is triplet ; it is situated beyond 

 the violet, between H and L, but very near the latter ; it is the re- 

 petition (so to say, the sharp harmonic) of the line b of the visible 

 spectrum, the wave-lengths being nearly in the ratio of 3 to 4. 



The experiment had succeeded a great number of times ; never- 

 theless I was desirous of repeating a series of measurements of refran- 

 gibility and wave-lengths with a more powerful pile and a very 

 effective induction-apparatus £. 



To my great surprise, the spark, really prodigious, produced 

 scarcely any photographic impression, relatively to what I had ex- 

 pected to obtain ; it was also necessary to prolong the time of expo- 

 sure to two minutes, it having been estimated, from the strength of 

 the spark, at two or three seconds. The examination of the plate 

 revealed an unexpected phenomenon : instead of the usual three 

 lines, there were five ; the two least refrangible were distinctly 

 doubled ; yet the lines were very broad, and their exterior contours 

 ill defined. My first idea was to suppose an error in fixing the po- 

 sition of the apparatus {mise an point); but on substituting iron elec- 



* Comptes Rendus, 1869, vol. lxix. p. 333 : " Methode optique pour 

 l'etude de la deformation de la surface exterieure des solides elastiques." 



t Comptes Rendus, 1869, vol. lxix. p. 337 : " Sur les spectres ultra- 

 violets/' by M. Mascart. 



§ A large induction-coil, fed by a pile of 16 Bunsen couples arranged as 

 8 elements with double surface ; condenser spherical, of 40 centims. dia- 

 meter; electrodes of magnesium, consisting of two pieces of metal of 10 

 millims. thickness. 



