408 Intelligence and Miscellaneous Articles. 



known to the peasants under the name of thunder stones. Generally 

 speaking they lie at a very small depth below the soil. 



PHENOMENA OBSERVED IN THE SPECTRA PRODUCED BY THE 

 LIGHT OF INDUCTION-CURRENTS IN TRAVERSING RAREFIED 

 GASES. BY M. J. CHAUTARD. 



In examining the spectra produced by rarefied gases raised to in- 

 candescence under the influence of the current of a Ruhmkorff's 

 coil, I have noticed various new phenomena. 



The degree of incandescence of the gas may vary either in conse- 

 quence of the greater or less density of the ponderable matter in the 

 tube, or from the intensity of the inducing current. M. Pliicker 

 has described the phenomena arising from variations in the elasticity 

 of the gas, but he has not examined the different conditions of the 

 spectra when the resistance offered to the current of the pile is made 

 to vary. 



This variation of resistance in the inducing current may be pro- 

 duced by two distinct methods — either by elongating the wire tra- 

 versed by the current, or by introducing a bar of soft iron into an 

 auxiliary coil which is traversed by the circuit of the battery which 

 works the Ruhmkorff's apparatus. 



Working so as to vary gradually the intensity of the pile, I ob- 

 served the following phenomena with the tubes at my disposal : — 



1 . The dazzling red light of the hydro gen-tuhe finishes by being 

 changed into a livid whitish-green tint ; the spectrum, instead of 

 offering three magnificent rays, red, green, and violet, which cha- 

 racterize this gas, and which occupy almost the position of the three 

 Fraunhofer's rays C, F, and G, only give a very pale green. 



The glass does not become appreciably heated in the hand. 



The stratification in the enlarged part of the tube has the same 

 appearance and the same precision as in the case of the normal current. 



In using only the external pole of the induction apparatus, the 

 current still traverses the gas, but the light becomes so pale that no 

 shading can be distinguished by the prism. 



2. In nitrogen the disappearance of several shades can be distin- 

 guished ; but here the vanishing of the colours seems to take 

 place in inverse order. Thus the rays of red and of orange first 

 become weaker ; the violet only disappears finally ; the yellow and 

 green rays remain, spite of the diminution of the light. 



3. The rays in carbonic acid are very numerous with the ordinary 

 current of the coil ; but if the tension of the inducing circuit is di- 

 minished, the same absorption of the extreme shades is noticed. 

 Red commences to disappear, then the violet rays, as well as the 

 green ray nearest the red. 



The external circuit used alone does not allow the shades of the 

 spectrum to be distinguished. 



4. Bromine gives a magnificent spectrum furrowed by about nine- 

 teen of the most beautiful rays separated by almost dark intervals. 

 The introduction of a resistance into the inducing circuit modifies 

 neither the nature of the spectrum nor the number of rays ; there is 

 seen only a simple enfeeblement in the general aspect of the tints, 

 which never completely disappear. — Comptes Rendus, Aug. 22, 1SG4. 





