208 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
inches. The current of 2400 cells was 0 ’01 04 7 W. The resistance of the 
tube was found, by substituting wire resistance for it, to amount to 210,000 
ohms at the time of the experiment, but several months before it had only a 
resistance of 18,000. In the small tubes were produced closely-packed 
strata, in the large central bulb were three umbrella-shaped strata much 
fainter; these moved towards the negative on introducing 50,000 ohms, a 
fresh stratum pointed at the apex entering the bulb from the right-hand 
tube (positive side), C. 0 '006 72 W. On introducing 20, 20, and 10 more 
thousand ohms, they retreated from the large bulb towards the positive. 
Tube 26, Hydrogen. 
201. — This tube is in form like 10, fig. 37 ; the length between the terminals 
23 inches. The first bulb has a major axis, 3*25 inches, a minor, 1*875 
inch, the tube joining this with the central bulb, 6 inches long, its internal 
diameter 0*44 inch; the central bulb has a horizontal major axis, 4*5 
inches, the minor being 2*25 inches ; the tube joining it to the third bulb 
is 5*5 long, its internal diameter 0*56 inch ; the major axis of the third bulb, 
3*5 inches, the minor, 2*125 inches. With 3240 cells, when the small tube 
was positive, C. 0*0073 ; when negative, 0*00481 W. When the small tube 
was either positive or negative it had 34 strata, while the large tube had 
had 25. The bulb on the positive side had three cup-shaped strata near the 
terminal, convex towards the negative. The central bulb had also three or 
four fainter pink strata, convex towards the negative ; the third bulb was 
filled with a pink negative glow. The strata in the two tubes were blue. A 
photograph was obtained in 25 seconds in August, 1875, but has not been 
engraved, and is another of those communicated to the Academie des 
Sciences of Paris. 
Tube 51, Hydrogen. 
201«. — This tube was constructed to show that the extent of the glow along the 
negative terminal was dependent on the strength of the current. The 
length of the tube is 6 inches, the diameter 2 inches. The negative 
terminal is a platinum wire 19 inches long, and about 0*025 inch in 
diameter, coiled into a horizontal spiral of four complete turns, concentric 
with the tube ; it is supported in its position by three fine glass rods 
running parallel to the axis of the tube. The positive terminal is straight, 
and extends vertically to the common axis of the tube and spiral. The 
distance between the last ring of the spiral and the positive terminal is 
f inch. As the strength of the current is increased, the glow which, with a 
current of 0*00238 W, illuminates only the 2 inches of the negative nearest 
