162 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
between D and C, the Z terminal of the battery being connected to D. When the 
resistance is greater or less than that of the tube to be tested there is an illumination 
in the detector tube between B and C ; but when a current passes in T T', balanced 
by a proper adjustment of the coil resistance, then the glow in the detector ceases. 
It was ultimately found that the detector tube might be suppressed because, as 
Fig. 38. 
soon as the resistance in B D is a little in excess of that of the tube, the 
latter gives evidence by its illumination of the current passing. After the current 
in a tube has commenced it is generally found that it will continue to glow, even 
when some of the balancing resistance, B D, is plugged out in the coil box, showing 
that when once started the working resistance becomes less. If, on the other hand, 
the current has been stopped entirely, it requires generally a greater balancing 
resistance in the coil box between B D to start it again than it did in the first instance. 
After standing for a short or long time it regains its normal condition, but the interval 
required may amount to several days. The following numbers were obtained : — 
