ELECTRIC DISCHARGE WITH THE CHLORIDE OF SILVER BATTERY. 199 
much heat developed in its immediate vicinity, the remainder of the tube 
being cool. 
168. — Gas was let in, and the pressure raised to 15 m.m., 19,737 M, 11,000 cells. 
No luminosity at the positive, but a faint one at the negative, not unlike 3, 
fig. 50, in general shape, but twice as long, without any markings of brighter 
light. 
169. — Pressure 13 m.m., 17,105 M, 11,000 cells. A serpentine line of light, 
extending from the positive wire right through the negative ring. In the 
rotating mirror a flow was observed towards the negative at very different 
velocities in different parts of the tube, being much more rapid in the half of 
the tube nearest the positive. 
170. — Pressure 7 ’023 m.m., 9240 M, 7760 cells. Current, when point was 
positive, 0‘02289 W, when point was negative, 0'02051 W. A photograph 
on a dry plate, obtained in one minute, showing 1 7 luminosities, like those 
in tube 129, at 4 m.m., 5263 M, fig. 7, Plate 15, Feb. 1, 1878. On March 
14th the luminosities were fifteen in number, whether the point or ring was 
positive. This tube was detached from the pump, in order to retain this 
particular phase. It bears a record of the position of the luminosities by a 
metallic deposit in the cooler spaces between them. 
Gassiot Tube 342, Hydrogen. 
171. — This most interesting tube was a favourite of our friend the late Mr. Gassiot, 
and was presented by him, with many others, to Mr. Spottiswoode. It 
retains, in a remarkable degree, the record of old stratification by bands of 
dark deposit with clear spaces between them. It was a matter of interest to 
ascertain whether the lines of deposit coincided with the position of the 
spaces or with that of the strata. This tube is composed of a cylinder 
13 inches long and l- x % inch in diameter, having at one end a bulb 
2 inches in diameter, from which project at right angles to the main tube 
two short lengths of tube 1-g- inch in diameter, the whole resembling in form 
the letter T. At the end of the tube opposite the bulb is a straight brass 
wire xg- inch in diameter screwed on to a wire of platinum, and in the 
head of the T a brass wire, 4f inches long, reaching axially right 
across. The bulb and short tubes attached to it are completely coated with 
a dense black metallic deposit, and for a space of 5 inches from the bulb the 
main tube is stained with eight dark bands. 2400 cells gave a current 
0 - 02289 W, the straight wire being positive and the cross wire in the bulb 
negative ; there were produced beautiful double strata intensely blue, like 
those in fig. 3, Plate 16, completely filling the tube. Strips of paper 
were fastened over these strata in the region of the stains ; these were found 
