783 
The pressurecoefficient was taken to be 0.0046 for an initial 
pressure of 84 atm. and 0.0042 for a pressure of 41 atm. These 
values were obtained by extrapolation from AMAGAT’s observations *). 
Hydrogen. 
7. The first series of measurements were made with double 
purified hydrogen, supplied by the “Oxygenium’’ Company ; analysis 
in a Hempen explosionbulb showed no impurity. With a view to 
absolute determinations measurements were subsequently made with 
a cylinder of very pure hydrogen which had been prepared in the 
Leiden laboratory by freezing out the impurities at low temperature. 
Measurements dated 24 to 294 of May with the first gas gave 
the following results: 
i AB I4E clk 
; ‚pressure | temp. |galv. deflect. > ;p_ 
a in AU. in atm. in °C. mm. — R/Racar 
| | 
4047 Belen 8 373.8 1.00 
| 
3665 56:60 OR 288.1 1.235 
sis sit |C 149 197.1 1.79 
2805- | 528 1.18.7 159.6 2.40 
2654 | 57.8 15.9 126.9 2,755 
2535 Bes ef 115.2 3.14 
2482 56.4 16.4 107.0 3.355 
The nicols were set beforehand at an angle of 92°. The exposures 
varied from 1.5 to 10 minutes. The pressurecoefficient was taken 
to be 0.0037 and no correction was applied for deviations from 
Borre's law. 
A higher pressure was obtainable with the Leiden hydrogen, and 
the nicols were accordingly set at an angle of 92°.5 for that series 
of measurements. Currents were measured with the ammeter already 
described. (range 0 to 50 amp, 1 scale division = 0,5 amp). 
The exposure for the last two ultraviolet lines 2399 and 2378 A.U. 
was 18 mts; the current was kept constant at 10 amp. for an hour. 
On account of the heating of the coils not more than three expo- 
sures could be made in any one series. The following-are the results 
of these measurements : 
1) WiitLNer. Experimentalphysik. 5te Aufl. Band Il. Tab. p. 138. 
