140 On the Use of Steam in Spectrum Analysis. 



charge from one terminal to the other. No spark could be 

 obtained and the experiments were abandoned. During the 

 present winter the experiments were renewed. The containing- 

 vessel was abandoned, and the jet of steam was allowed to 

 impinge directly upon the spark. No effect could be per- 

 ceived when there were no condensers in the secondary 

 circuit, and with the introduction of small condensers the 

 effect was not marked. When the number of Leyden jars 

 (8 in. X 6 in.) was increased to four, the effect of the jet of 

 steam upon the electric spark was surprising. Its light 

 immediately became comparable with that of the electric arc, 

 enabling one to see metallic spectra with the naked eye upon 

 the ground -glass of the photographic camera without the use 

 of an eyepiece. The chamber in which the spark and steam- 

 jet was placed became rosy red from the hydrogen arising 

 from the dissociation of the steam. The hydrogen and 

 oxygen lines in the air-spectrum became very much 

 strengthened ; a continuous spectrum showed itself in the 

 neighbourhood of the C line, and also in the yellow. A pho- 

 tograph of the air-lines and metallic lines of the terminals 

 employed could be taken in a third of the time which was 

 necessary when the steam-jet was not employed. 



The apparatus consists merely of a tin box which is placed 

 opposite the slit of the spectroscope. Steam enters at one 

 side and is blown across the terminals of the Ruhmkorff coil, 

 which are placed in the box opposite the slit. An outlet on 

 the side opposite to that in which the steam enters allows 

 the steam to escape into the outer air. 



The change of colour of the spark is undoutedly due to 

 hydrogen. The light filling the box is decidedly red, and the 

 hydrogen-line C flashes out with great brilliancy in the midst 

 of a continuous band of red in the spectrum. The metallic 

 lines of the terminals are also greatly strengthened. The 

 light from iron terminals is especially brilliant. Without the 

 steam the spark between iron terminals seems to consist of a 

 single line of discharge. When the steam is turned on, a 

 great bundle of sparks appear in the midst of a flaring light 

 and the noise of the sparks was greatly increased. These 

 effects can undoubtedly be attributed to increased conducting 

 power of the air-space between the terminals of the Ruhmkorff 

 coil. 



The appearance of the spectrum led us to examine the 

 question of the character of the spectrum of the aurora 

 borealis and its connexion with that of aqueous vapour. 

 We believe that the theory that the shifting nature of the 

 northern lights may be due to electrical discharges following 



