422 
We see that the double refraction approaches asymptotically a 
maximal value. 
The electric double refraction of ammonium chloride is thus proved 
to be not proportional with the square of the intensity of the field. 
For if it were so it should have to show a same dependency on the 
field in an alternating field. Since this is not the case however the 
dependency on the field cannot be derived from the above curve, 
also by the uncertainty where in this case of the 50 alternations 
per second the band of the bead will appear; for the band follows 
the alternations, as has been proved by means of a stroboscopic 
method. 
Therefore an investigation in a constant field was required. For 
this purpose the electric arrangement sketched in fig. 2 was used, 
with a few changes in the case of weaker fields. The observations 
were made photographically. 
Again one plate was exposed four times with one and the same 
cloud: first without fieid and then with the tensions V,, V, and V,. 
In the same way as above, the plates were again developed ete. 
and then the distances were measured. Now too measurements were 
made for a series of different clouds, the results of which were 
eter a1 ~ & while = has been put = 50 
| sometimes = 530 volt | 
TV a 
| 210 18 19 | 
| 210 20 23 | 
| 240 33 35 | 
| 270 36 49 | 
| 330 | 34 36 | 
‘ 810 71 74 | 
| 925 54 59 | 
990 | 56 63 | 
1050 | 54 60 | 
1360 see 57 61 
| 1900 | 62 68 
| 1970 | 67 69 
| 2280 | 54 65 
3400 Si 68 
