lines 

 rono-n 



744 Prof. li. W. Wood on Hydrogen Spectra 



In both helium and argon, without a condenser the appear- 

 ance of the discharge in the rotating mirror differed from 

 that observed in tiie casa of hydrogen. With the latter 

 gas, the broad bands of light were furrowed by sinuous dark 

 (the dark spaces between the striae) which may be 



ghly indicated thus |u|!||||. The wavy form 



•J *.) \j «.«.<■ «.-■ 



indicates that the striae oscillate slightly to and fro during 

 the half cycle. 



With argon and helium, however, we frequently have 

 broad bands of light thickly speckled with small bright 

 patches arranged apparently in a perfectly irregular manner. 

 With, less current we observe in the mirror a large number 

 of striated discharges very close together, possibly $.0 or 100 

 in each half cycle. The stria? are not exactly " in step," 

 consequently when the discharges occur so rapidly that the 

 mirror no longer resolves them, instead of having wavy lines 

 (as with hydrogen) we have an irregular speckled appearance. 

 This phenomenon will be further investigated and reported 

 in a subsequent paper. 



Argon and helium are the only two gases which, up to the 

 present time, have been observed to give discontinuous dis- 

 charges in the absence of a condenser. With a suitable 

 capacity we may have an initial discharge of a violet colour 

 (non-striated) followed by a large number of pink or light 

 red partial discharges, (striated) easily separated by the 

 mirror. These phenomena can all be seen in a mirror held 

 in the fingers and waggled rapidly up and down. 



With a large capacity (12 jars) the initial discharge is 

 white and the following partial discharges light red. An 

 initial discharge of characteristic colour always heads the 

 discharge of each half cycle, showing that the gas recovers 

 its normal condition during the brief period of repose 

 between the half cycles. 



Summary and Conclusions. 



In a tube of great length, containing hydrogen with a 

 suitable trace of water-vapour, the centre of the tube exhibits 

 the Balmer series, with the secondary spectrum reduced to 

 ^q of its usual intensity. The ends of the tube (to a 

 distance of about 40 cms. from the electrode bulbs) show the 

 secondary spectrum strongly developed in addition to the 

 Balmer series. The phenomena are of the same nature with 

 a continuous current of high potential as with the alternating 

 current from the transformer, ?'. e., the secondary spectrum 

 develops at both the anode and cathode. I have no explana- 

 tion of these peculiarities to offtr. With the tube in this 



