The Bending of Magnetometer Deflexion-Bars. ag 
Résumé. 
1. The sensibility of selenium cells, containing highly 
purified selenium mixed with various metallic selenides, was 
examined in different parts of the spectrum, and it was 
found that the position of the maximum, near ()°7 w, remained 
fixed. It was concluded that the position of the maxi- 
mum was not governed by the metal in the selenide, but 
probably by the free selenium itself. 
2. It has been shown that a selenium cell, taken from 
darkness into light and again returned to darkness, under- 
goes changes in resistance whether an electric current flows 
or does not flow through the cell. 
3. A suggestion as to the possible action of a selenium 
cell has been made. It is supposed that light affects the 
selenium directly rather than the selenide. This explana- 
tion, expressed of necessity in rather indefinite terms, gives 
promise of accounting for certain phenomena, the explanation 
of which fails at the hands of the existing theory. 
This investigation has been carried on during the past 
year under the supervision of Professor C. E. Mendenhall, 
to whom | wish to express my warmest thanks for his many 
valuable suggestions, and for the kindly interest he has taken 
in the progress of the work. 
Physical Laboratory, 
University of Wisconsin. 



V. The Bending of Magnetometer Deflexion-Bars. By 
C. Curet, Se.D., LDLLD., F.RS. (From the National 
Physical Laboratory.)* 
‘a May 1901 I communicated to the Society a paper f 
making various applications of Elastic Solid Equations 
to Metrology. Amongst the examples treated was the 
bending of magnetometer deflexion-bars. As explained 
(1. c. pp. 613-615), the deflecting magnet is carried by the 
deflexion-bar at an appreciable height above the c.«. of 
the cross-section, and the bending of the bar when in use, 
under its own weight and that of the magnet with its carriage, 
results in an increase of the distance between the deflecting 
and deflected magnets. To keep the instrument properly 
level, there ought to be a counterpoise on the other arm of 
the deflexion-bar, at the same distance as the deflecting 
magnet from the centre. In the absence of such a counter- 
poise, supposing the instrument originally level, the weight 
* Communicated by the Physical Society : read October 23, 1903. 
+ Phil. Mag. [6] vol. ii. pp. 582-558 & 594-616. 
