508 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
Divisions. 
Ratio to tube 
potential = 1. 
1 . 
Idle wire, T potential 
48 
= 0-52 
Tube 
5 ) 
92 
1 . 
A little higher exhaust, T 
55 
57 
= 0-60 
Tube 
55 
95 
2 . 
T 
5 ? 
118 
= 0-87 
Tube 
55 
136 
2, 
A little higher exhaust, T 
55 
CO 
= 0-93 
Tube 
55 
144 
3. 
T 
55 
143 
= 0-90 
Tube 
55 
158 
4. 
T 
55 
170 
_ 0-94 
Tube 
181 
5. 
T 
55 
163 
= 0-95 
Tube 
55 
173 
It is evident, therefore, that as the exhaust increases, and the luminous spindle 
becomes more developed, the potential of the idle wire, T, augments until it nearly 
or quite equals that of the whole tube. 
In tube No. 3G3 there was no means of testing the potential on the outside of the 
negative ring under the same conditions as the centre, so that another tube, No. 364, 
was made in which an idle wire, T, was in the axis 0'25 inch (0'63 centim.) from the 
jolane of the ring, and another, T', 0T5 inch (0 - 38 centim.) from its periphery. The 
tube is 13f inches (34‘3 centims.) long, If inches (4'44 centims.) in diameter, and 
inches (24*1 centims.) between the terminals, and was charged with carbonic 
anhydride. 
When 2400 cells were used, the tube potential was found to be 742 cells; the 
potential of the axial wire, T, was 158 cells, when that of the exterior wire, T', was 
only 40 cells, so that the potential of the central wire, T, xvas f^-=3 , 9 times that of 
the external wire T'. The potentials in relation to that of the whole tube equal 1, 
were found to be T wire = 0*21, T' = 0'054. 
Potential across a dark space and a stratum respectively. 
At the suggestion of Professor Stokes, experiments were made to ascertain the 
potential across a dark space and also a stratum, several tubes being constructed for 
that object. The experiment is an extremely troublesome one, on several accounts; m 
the first place it is difficult to get a stratum or a space to fall exactly between a pair 
