781 
rm 
16 atm.'). Equal intensities for the line 3130 (in the centre of 
the plate) occur between the 4® and 5 exposure from above. The 
variation of the current was */, amp. 
Fig. 4. 
As the ammeterreadings, or the galvanometerdeflections corrected 
to angular deflections, are, for constant gasdensity, inversely propor- 
tional to the required Verpet’s constants, the relative rotatory con- 
stants can be calculated from such photographs; in this the constant 
for the violet line 4358 A.U. is usually chosen as unity. The relative 
rotation is then obtained from: 
a Vi FF; (ty 
1) The line 2805 is the second from the right, not the first as is erroneously 
shown in the figure. Horizontal distances are magnified four times, and vertical 
distances about seven times. Differences in intensity are indicated by differences 
in breadth. 
