388 Intelligence and Miscellaneous Articles. 



tubes have been made by E. Wiedemann (Wied. Annalen, vol. vi. 

 p. 298, 1879, and vol. x. p. 202, 1880), and by M. Nasselberg 

 {Mem. de VAcad. Imp. des sciences de St. Petersbourg, vol. vi. No. 1, 

 1879). M. G. Staub further has recently (Inaugural dissertation, 

 2nd part, Zurich, 1890) made some experiments on the development 

 of heat in the discharge of Leyden jars through Geissler's tubes 

 filled with air and hydrogen : he has at the same time attempted to 

 determine the ratio of the obscure to the luminous radiation. 

 "With this view he enclosed the tube in a Bunsen's ice-calorimeter, 

 where the tube and the calorimeter successively transmitted or 

 absorbed the luminous radiation ; in the latter case the tube was 

 blackened. 



Not only the total energy absorbed by the gas and that radiated 

 have been measured in these experiments, but also the energy 

 received directly from the sides of the tubes, and which 

 they chauged into heat. However valuable these researches 

 may have been, they do not give a direct answer to the question of 

 the radiation of the gas under the action of the electric discharge. 

 A direct determination of this intensity has not yet been made 

 so far as I know, and the possibility of such a determination, 

 with our present resources, has even been questioned. For this 

 reason I have endeavoured to use the bolometer to determine the 

 radiation of different gases under the action of the electrical 

 current ; to express the intensity of this radiation in absolute 

 measure ; and to endeavour then to determine the relation of the 

 radiation to the causes which produce it. 



After having worked for more than a year at this very arduous 

 investigation, I think I may consider that the preliminary trial 

 experiments are completed. I shall explain here some of the 

 results at which I have arrived ; treating afterwards with greater 

 detail the materials which I have collected. 



II. As the light of the kathode is too feeble and its shape too 

 variable to justify the hope that I could obtain very accurate 

 quantitative results, I restricted myself to the investigation of the 

 positive light only. 



I used cylindrical glass tubes of the same thickness and 10 to 

 15 mm. in diameter. The electrodes were usually placed in 

 side tubes at right angles with the principal tube. One end of 

 the tube and sometimes both were closed by a smooth plate of rock- 

 salt fixed hermetically by means of siiicate of soda. In the pro- 

 longation of the axis of the tube a sensitive bolometer was placed, 

 separated from the tube by a double screen with apertures in the 

 direction of the axis of the tube. Between the sides of the screen 

 was another double movable screen. 



The indications of the bolometer were compared with one of my 

 instruments for determining radiant heat in absolute measure 

 (Acta Beg. Soc. Upsal. series iii. 1886. See also Ofversigt af Kongl. 

 Vet.-Ahad. Forhandl. No. 6, p. 379, 1888). I found in this way 

 that one division of the scale corresponded to a radiation of 

 278 X 10 -9 gramme calories per second and square centimetre. 



