174 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
shown in 2, fig. 43. The tube became very hot * in the immediate neighbour- 
hood of the luminosities, which were very steady, but was much cooler 
at the negative and positive terminals, especially at the latter. 
11. — Pressure 13 m.m., 17,105 M, 8040 cells. Luminosities were produced as the 
right hand diagram in 2, fig. 43 ; these were very blue, accompanied with great 
heat in their neighbourhood. In the rotating mirror the flow was seen to be 
towards the negative. 
12. — The following day, the pressure being still 13 m.m., 8040 cells gave inter- 
mittent worm-like luminosities, 4, -fig. 43, with the point negative : these did 
not occur when the point was positive. 
13. — Pressure 12‘2 m.m., 16,053 M, 8040 cells. The luminosities as in 5, fig. 43, 
when the point was negative. The flow of the luminosities was shown by 
the rotating mirror to be towards the negative. There was much heat 
developed in the neighbourhood of the luminosities, but little heat at the 
positive terminal, while the negative remained quite cool. 
14. — Pressure 10'8 m.m., 14,211 M. Luminosities as in 6, fig. 43, which reminded 
one of a fish’s mouth, especially as they opened and closed continually : they 
extended along 9 inches of the tube. 
15. — Pressure 7’5 m.m., 9868 M, 8040 cells. 10 luminosities like the right-hand 
of diagram 2, fig. 43, but more pointed, the apex being agitated like the 
preceding fish-mouths. 
16. — Pressure 6 m.m., 7895 M, 5640 cells. The luminosities still more pointed; 
there was heat in the vicinity of the luminosities : 3240 just passed but the 
luminosities were confused. 
17. — At a pressure of 1 m.m., 1316 M, the most beautiful phase of all was pro- 
duced as shown in fig. 44, in some of its chief features ; the current used 
was that of 2160 powder cells, (C.) 0 , 011520 W. The strata grouped 
themselves in threes and reached to within 6 inches of the negative ring ; 
when 200,000 ohms resistance was introduced, (C.) 0'005658 W, the dark space 
extended to 9 inches. Only a portion of the luminosity about the negative 
ring is shown in the diagram ; besides this, the ring was surrounded with a 
* De la Rive (Archives Sci. Phys. Nat., xxvi., pp. 202-207) investigated the temperature of 
rarefied gases during the electric discharge. He employed a tube 160 m.m. long and 40 m.m. in diameter, 
with copper halls 10 m.m. in diameter for terminals. A pair of thermometers, whose mercury reservoirs 
were cylinders 30 m.m. long and 2'5 m.m. in diameter, were inserted each at a distance of 10 m.m. from 
its terminal. The conclusions drawn by him from his experiments are (i) that a sensible elevation of 
temperature accompanies the discharge in rarefied gases ; (ii) that this elevation is sensibly less in the 
neighbourhood of the negative than near the positive electrode, provided that the gases are sufficiently 
rarefied, that the discharge passes easily, and that the light is stratified ; (iii) that the absolute elevations 
near the two terminals and the differences of elevation vary with the density and nature of the gas. 
De la Rive remarks that these investigations are not to be confounded with those which have been 
made by Gassiot concerning the temperature of the terminals themselves, 
