245 
which is low enough even for galvanometers of small resistance. Of 
course one can also use wider strips. 
It is not possible to use these thin strips as a suspension, for they 
show the small torsional rigidity only when unstretched. Therefore 
I use a quartz fibre suspension taking care that this produces 80 
or 90°/, of the required torque. As a consequence the elastic 
after-effect of the strips which is otherwise considerable, is of little 
or no importance. The metal strips — probably copper is in some 
respects to be preferred to silver — hang loosely on both sides of 
the quartz fibre. 
Finally 1 will mention the fact that the very light moving systems 
of my galvanometers appear to be little sensitive to tremors. Surely 
this is at least partly due to the relatively strong air-damping which 
makes the vibrations about horizontal axes decay pretty quickly. 
Groningen. Physical Laboratory of the University. 
