756 
In this formula the currents must be known with the same rela- 
tive accuracy. As the rotation by water for the mercuryline 4358 
A.U. is about 25,3 times greater than for hydrogen(100 kg/em? 17.°5), 
the ammeter ranges used were 0 to 2 and O to 50 amp. After 
filling the experimental tube with water I found, contrary to expec- 
tation, that the 230 em. column transmitted the ultraviolet only up 
to the wavelength 3665 A.U., while Lanpavu with a waterlayer of 
1 em. was still able to obtain photographs of the iron line 
2496 A.U. I finally used only the line 4358 for these measurements. 
The exposures were two minutes for hydrogen and five for water. 
On account of the repeated fillings of the experimental tube the pres- 
sure obtainable from tbe Leiden cylinder of hydrogen sank to 
75 kg/em?, so that the currents used for the gas were about 34 
times those required for the water photographs. 
In this way I obtained for 
Hydrogen (73.9 atm. 16°.9.) /y = 37.72 amp. 
Distilled water ly —=1.145 amp. 
According to SIERTSEMA Ryy = 0.02495’ for 2= 4358. From my 
measurements we may calculate /7= 32.88 amp. for a pressure 
of 85 ke and a temperature of 9°.5, whence it follows, that /?77(85 
Au ER 
