Intelligence ci7id Miscellaneous Articles. 389 



To ascertain if and how far the character of the radiation changes 

 with the different conditions of the gas, I measured on the one hand 

 the total radiation, and on the other the radiation transmitted 

 by a plate of alum of 3*95 mm. in thickness. The radiation 

 determined by direct observations consists of two parts — the 

 radiation of the gas, and that of the more or less heated sides of 

 the tube. The latter part must be eliminated, which is effected by 

 a series of observations of the radiation of the tube after the 

 current has been opened. From the curve of radiation thus found 

 it is easy to calculate the radiation of the tube during the experi- 

 ment, and by subtracting this quantity from the quantity observed 

 during the passage of the current the radiation of the gas is 

 obtained. This value, however, is increased by the reflexion of 

 the sides of the discharge-tube, and diminished on the other hand 

 by the reflexion of the plate of rock-salt which closes the tube. 

 Direct experiments, the details of which I suppress, have enabled 

 me to make a satisfactory correction for this reflexion, and therefore 

 to determine the total radiation in absolute measure. 



As source of electricity 1 principally used an accumulator of 800 

 elements of Plante's pattern, and also a Bnhmkorff's coil of medium 

 size. The current was determined by a dead-beat reflecting- 

 galvanometer, with a wire insulated by caoutchouc. The diff- 

 erence of potential between two points in the positive light was 

 measured by means of two thin platinum wires, soldered in the 

 discharge-tube, and connected with a Mascart's quadrant-electro- 

 meter. For exhausting the tube I used, in my later experiments, 

 a pump on Sprengel's principle, modified by Prytz (Wiedemann's 

 Annalen), and further improved by myself. 



I have spared no pains to make the gases as pure as possible. 

 Thus neither stopcocks, nor caoutchouc tubes, nor grease were 

 used either in the preparation of the gas or in the connexion of 

 the tube with the air-pump. To introduce the gases into the dis- 

 charge-tube, to dry them, and to prevent the access of mercurial 

 vapour to the tube, I used the method of M. Cornu {Journal de 

 Physique), slightly modified for my purpose. My researches 

 extended to oxygen and hydrogen liberated by electrolysis of pure 

 water acidulated by phosphoric acid ; to nitrogen produced by 

 leading pure air freed from carbonic acid over heated copper (first 

 reduced by hydrogen) ; and to carbonic acid produced by heating 

 sulphuric and oxalic acids and purified by passing through a solution 

 of potash. 



III. I give here the most important results of this research. 



1. For a given pressure, the radiation of positive light is pro- 

 portional to the intensity of the principal current. It is true that on 

 using very powerful currents small divergences are observed, but 

 in this case they are always accompanied by a permanent alteration 

 of the gas, so that the same radiation is not met with again for 

 less strong currents. 



2. If the electric current is kept constant and the pressure is 

 varied, it appears that the intensity of total radiation scarcely varies 



