during the passage of the Electric Discharge. 1 5 



situated on the extreme boundary of the red, the second is reddish 

 orange, the third greenish yellow, the fourth green, the fifth blue, 

 and the last violet. Both of the two first spaces are divided into 

 three equally broad subdivisions by narrow black-grey bands, 

 of which two always border upon the bright band. The fu-st 

 space is brown-red, the second dirty-orange and yellow. The 

 third and fourth spaces are of a rather faded green, and much 

 subdivided by diflPerent degrees of shading. The fifth space, 

 which is very faded, is divided into two equal spaces, which are 

 shaded off from the red side towards the violet. After the last- 

 mentioned violet band, another dark portion of the spectrum 

 occurs about as wide as the red-yellow portion. In this dark 

 portion three spaces are separated by three prominent and well- 

 marked violet bands, whose breadth is of the same value as that 

 of the before-mentioned six bands. The last of these violet 

 bands forms the visible boundary of the spectrum. The first of 

 these three spaces, which is contiguous with the above six bright 

 bands, is somewhat broader than the third. Both are perfectly 

 black. The second and middle space is about as broad as the 

 first and third together, and is of a very dark violet colour. 



The first band, which at the moment of commencing was of 

 an especially brilliant red, lost almost the whole of its brightness 

 after the stream had passed through the tube for a long time (115). 



The light of the galvanic current in the narrow tube was 

 greenish-white. 



105. After the spectra of the three above-named gases had 

 been accurately determined and copied, the double tube repre- 

 sented in fig. 2 was filled with two different gases, carbonic 

 acid aud hydrogen, and then exhausted as far as possible. The 

 gases, which were originally separated from one another, could 

 be put into communication by means of a cock. This was done 

 while the stream passed simultaneously through both tubes, 

 through the one with a greenish-white, through the other with a 

 red light, and while the spectrum of the one gas (the carbonic 

 acid) was observed through the telescope by the prism.. Imme- 

 diately on opening the cock, a dazzling red line was at first seen 

 merely flickering now and then at the boundary of the spectrum. 

 It soon took up and maintained a constant position: this was 

 the red band of the hydrogen gas. The colour of the light in 

 the two narrow tubes was the same ; the two spectra had become 

 constant and identical in kind. 



Universally, if two different gases are mechanically mixed in 

 a tube, and the two spectra of the separate gases are known, it 

 is easy to see how the spectra of the separate gases overlap one 

 another, forming the spectrum of the mixed gas. 



lOG. Next, a single tube was filled with ammonia and ex- 



