276 SCIENCE PROGRESS. 



in the capillary and near the poles were changed. From 

 the capillary there was but a feeble glimmer, not of an 

 orange tint, while the orange tint was now observed near 

 the poles, the poles themselves being obscured by a coating 

 on the glass of brilliant metallic lustre. 



After attempting in vain for some time to determine the 

 cause of the inversion of D 3 and 447 in various photographs 

 I had obtained of the spectra of the products of distillation 

 of many minerals, it struck me that these results might be 

 associated with the phenomena exhibited by the tube, and 

 that one explanation would be rendered more probable if it 

 could be shown that the change in the illumination of the tube 

 was due to the formation of platinum compounds, platinum 

 poles being used. On 2 1st May I accordingly passed the cur- 

 rent and heated one of the poles, rapidly changing its direction 

 to assure the action of the negative pole, when the capillary 

 shortly gave a very strong spectrum of hydrogen, both lines 

 and structure. A gentle heat was continued for some time, 

 and apparently the pressure in the tube varied very con- 

 siderably, for as it cooled the hydrogen disappeared and the 

 D 3 line shone out w T ith its pristine brilliancy. The experi- 

 ment was repeated on 24th May, and similar phenomena 

 were observed. 



Some little time after 1 Professors Runge and Paschen, 

 from an entirely different standpoint, arrived at exactly the 

 same conclusion. 



The employment of exposures extending over seven 

 hours has given a considerable extension in the number of 

 lines, and the bolometer has been called in to investigate 

 lines in the infra-red ; better still, they have employed well- 

 practised hands in searching for series of lines. Operating 

 by chemical means upon a crystal of cleveite free from any 

 other mineral, they have obtained a product so pure that 

 from these series there are no outstanding lines. Very 

 great weight, therefore, must be attached to their conclusions. 



As a result of their investigations Drs. Runge and 

 Paschen stated that the gas given off even by a pure crystal 



1 Nature, 26th September, 1895. 



