( 840 ) 
TABLE 1. 
greater than -{- 1,75', but they still admitted of exact measurement. 
The above-mentioned change of sign is analogous to that found by 
Ingersoll in the infra-red and presents a characteristic and theoretic¬ 
ally important phenomenon. 
The relation between the rotation and the field was also investigated, 
and the results are shewn in Table 2 and Fig. 3. For low values 
of the field the two are proportional to each other, the rotation 
TABLE 2. 
afterwards assuming a maximum value, which remained nearly 
constant for further increase of the field. Considering, the form of 
the curve t = funct (*» and accepting the results previously found 
