during f he passage of the Electric Discharge. 13 



a piece of board, so that the narrow parts of both (at the parts 

 where they are bent at an angle of rather more than 90 degrees) 



Fig. 2. 



touch one another, and have exactly the same direction. (The 

 glass cock given in the figure has reference to a subsequent ex- 

 periment.) On discharging a curi'ent through such a system of 

 two different tubes, a straight thread of light appears in the 

 narrow part, which is broken only in the middle, and half of 

 which belongs to the one gas, half to the other. However dis- 

 similar the spectra of the two gases might be, any one colour of 

 the one spectrum (in those cases where it was not extinguished) 

 was contimied in a straight line in the other one; this was usu- 

 ally accompanied by a change in its brightness. 



100. In observing the spectra, I employed a Fraunhofer's 

 telescope, which was set up at a distance of from 4 to 5 metres 

 from the vertical line of light in the tube. The flint-glass ])rism, 

 whose refractive angle was 45 degrees, was fastened immediately 

 before the object-glass, whose aperture was 15 Paris lines. The 

 magnifying power of the eye-glass was so chosen that an increase 

 in its power did not show an additional number of narrow lines, 

 but only diminished the intensity of the light. 



The combination of two glass tubes described in the prece- 

 ding paragraph is capable of another application. If, namely, 

 the telescope be directed to the part where the narrow tubes meet, 

 the spectra of the two separate gases, being seen at the same 

 time, may be compared with one another, and the respective sizes 

 of the different parts measured. The spectrum of hydrogen 

 seems to me to be the most suitable, of those as yet examined, for 

 a standard of comparison, on account of its peculiar constitution. 



101. The tubes which I first examined were originally filled 



