164 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
Eig. 39. 
TUBE. 141. 
°^<kA A I A Kkkk kAkk A lAJAUI A A 1 1 lAUU/llAAAAAAAMl WWVWVW HBb 
Eig. 40. 
Tube 25 (C0 2 ) with 12 rings (not 11 as in fig. 37) 1 inch apart and 1200 cells. 
Between terminals. 
Numbers 1 to 3 1 to 4 1 to 6 1 to 7 1 to 8 1 to 9 1 to 10 
Relative distances 1 1-533 2-667 3‘267 3'867 4'533 5-198 
Relative resistances 1 1"035 1T09 1T09 1"274 L368 1-417 
Spottiswoode tube (No. 147, C0 2 ) and 3240 cells. 
Between the terminals at various distances from 7 to 49 inches. 
Relative distances 1 1"86 2"7l 3"57 4 - 43 5-29 6-14 7"00 
Relative resistances 1 1"24 1"24 1"49 1*35 l - 63 1"78 2 - 10 
Thus, for five times the distance the resistance, the mean of 1-9 and 1-10, is in 
tube 25 only 1'43, and in tube 147, 1‘54 ; for seven times the distance the resistance 
is in tube 147, 2*1. The degree of exhaustion of these two tubes is not known, 
but the internal pressure is, probably, less than 1 millimetre. 
In making these experiments it was noticed that the resistance for equal distances 
appeared to be greater in proximity with the negative pole than in other parts of 
the tube, and fresh experiments were in consequence undertaken to ascertain the 
potential at the several rings by means of a delicate Thomson-Becker quadrant 
electrometer furnished with an induction plate, I, fig. 41, which may be adjusted 
to any required distance from the quadrant beneath it. The tubes employed among 
others were No. 25, described above, and two other longer tubes, namely, No. .149 
(C0 2 ) with 12 rings 2 inches apart, and No. 150 (C0 2 ) with 17 rings also 2 inches 
distant. The current was led through a metallic resistance to the first ring, the 
last ring and the other pole of the battery being to earth. It was found that the 
greatest difference of potential occurs between the last ring and the last but one on 
the negative side, the next greatest difference being between the last and the last but 
the influence of distance between the terminals varied according to the degree of rarefaction. Eor 
instance, he joined, side by side, two similar tubes, in which the distances between the terminals were 
relatively 12 : 1, and exhausted them together. The two terminals of the one tube were connected 
respectively to the two terminals of the other, and a galvanometer could be thrown into the circuit of 
either tube. He found that at notable pressures the discharge was exclusively across the smaller space : 
but at 0"5 m.m. his galvanometer did not show any difference in the currents which traversed the two 
tubes. Schultz (Pogg. Ann. cxxxv., 1868, pp. 249-260) states that about that pressure which requires 
least difference of potential to produce discharge, the influence of distance between the electrodes is 
such that this difference of potential varies nearly in direct proportion to this distance ; but when rare- 
faction is carried beyond that point, and the difference of potential necessary to produce discharge 
rapidly increases, the influence of distance between electrodes rapidly becomes inappreciable. 
