376 



De La Rue and Muller. 



[May 16, 



in the neighbourhood of the luminosities, a little heat at the positive 

 terminal, the negative being quite cool. 



Pressure 108 millims., 14,211 |V|. Luminosities as in 6, fig. 1, 

 which reminded one of a fish's mouth, especially as they opened and 

 closed continually ; they extended along 9 inches of the tube. 



At a pressure of 1 millim., 1,316 |V|, the most beautiful phase of 

 all was produced as shown in fig. 2, in some of its chief features, the 

 current used was that of 2,160 powder cells, current 0*011520 Weber. 

 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 VV? ^ ne 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 cylindrical 

 nebulosity of about a J inch in diameter, and a glow filled up the end 

 of the tube. 



Fig. 2. 



Tube 161, Hydrogen. 



The difference of the strata in tubes of different diameter at the 

 same pressure and with the same current is very clearly brought out in 

 tube 161, fig. 3, composed of two portions, one being 18 inches long and 

 1*65 inch internal diameter, the other 17'5 inches long and 0'975 inch 

 diameter, the ratio of the sectional areas being 2*864 to 1. The ter- 

 minal in the small tube is a point, in the large one a riug. With 

 4,800 cells, the point (small tube) positive, C. 0*02825 W> there were 

 produced in the small tube 62 disk-shaped strata, and in the large tube 

 twelve cup-shaped strata occupying half of the length of the large tube ; 

 beyond these the discharge was dark. With the point negative 

 C. 0*02451, there were produced in the small tube 54 disks, and in 

 the large tube thirteen cup-shaped, completely filling it. The number 

 of strata does not therefore appear to be in the inverse ratio of the 

 areas. The strata in the small tube were blue, but at times, with a 

 larger current, carmine, as in the capillary part of a spectrum analysis 

 tube, the strata in the large tube being much fainter and pink. 

 62a and 625, fig. 3, copied from photographs obtained, the former in 

 15 seconds, the latter in 10 seconds, show respectively the appearances 

 at another phase, when the small tube was positive or negative respec- 

 tively. . . 



