﻿402 Dr. Genevieve V. Morrow on Displacements in 



2 seconds' exposures gives lines which show a great displace- 

 ment towards the red when compared with those of the arc 

 spectrum of brass when a weak current is used. With an 

 exposure of 30 seconds the displacement is increased in all 

 the lines, which is still the case on exposing for 2 minutes ; 

 but in the latter case the line \ 3282 has not such a large 

 wave-length as with an exposure of 30 seconds. 



Table II. contains the measurements of the zinc lines 

 \ 4810-7 and \ 4722-3. 



There is no displacement observed in the arc spectra with 

 increase of current when pure zinc electrodes are used, 

 which was also the case with the other zinc lines previously 

 examined. Both lines are reversed with a current of 4 

 amperes, and although the lines are nebulous when 12 and 

 18 amperes are used, still the reversed part is in every case 

 quite sharp and easy to measure. Eder and Valenta give 

 \ 4810*71 and X4722-26 as the wave-lengths of these lines, 

 which are considerably smaller than those given by Exner 

 and Haschek. In the spark spectra there is a displacement in 

 each line towards the red when compared with the arc spectra ; 

 the differences between the measured wave-lengths for each 

 line for the two different exposures lie within the limits of 

 error in measurement. The limit which has been taken 

 above for displacements is reached for one line by an ex- 

 posure of 30 seconds, for the other by 3 minutes' exposure. 

 Both lines are un symmetrically broadened towards the red, 

 the darkest part of the line in each case being almost on the 

 edge of the violet side, whilst the line itself gradually shades 

 off to the red. The increase in the time of exposure pro- 

 duced no alteration in the measured wave-lengths. 



The wave-lengths obtained for these two blue lines of zinc 

 when the arc spectrum of brass was photographed, showed 

 practically no deviation from the wave-lengths given by pure 

 zinc. Even when the current is increased to 18 amperes 

 there is no change in the wave-length, which is contrary to 

 the results obtained from the five lines described above. In 

 the table it will be noticed that there is a great difference 

 between the intensity of the lines when 17 and 18 amperes 

 current were used, which is accounted for by the fact that 

 there was a screen before the condenser lens in the one case 

 which cut off part of the light from the slit. From this it 

 can be seen that the change in intensity causes no difference 

 in the wave-lengths obtained. On using a current of 18 

 amperes the lines were very broad but the reversals were quite 

 sharp. The spark spectra obtained from brass electrodes 



