June 26, 1S79] 



NATURE 



201 



indistinct. In tlie rotating mirror the distinct strata were 

 steady, but in the indistinct portion there^ was indicated 

 a rapid flow towards the positive. _ The lines C, F, and 

 G seen in the glow around negative terminal, but C Snd 

 G were not seen in the strata. . ■ . . - 



Pressure r2 mm., i,579 M, 2,400 cells, C. 0-03251 W- 

 1 1 narrow strata, umbrella-shaped, about | of inch wide, 

 followed by two about ij inch wide, then a confused ; 

 discharge, in which the rotating mirror showed a rapid 

 flow towards the positive. C, F, and G lines visible in 



Fig. is. 



the negative glow ; G and C disappeared in the strata, 

 and F was very faint. 



Tube 139, Hydrogen.— VrtssMte 6'3I9 mm., 8,314 M, 

 8,040 cells. Three arrow-headed luminosities as depicted 

 in Fig. 3 in the Plate, copied from a photograph and a 

 drawing made at the time. The photograph was obtained 

 in 2 seconds. 



Pressure 9-502 mm., 12,526 M, 6,960 cells. One lumi- 

 nosity of which a photograph was obtained in 10 seconds 

 but has not been copied. Another photograph obtained 



Fig. 16. 



in I minute is shown in Fig. I in the Plate, it will be 

 observed that it has a spear-head continuation towards 

 the negative. ,, . ,, . , 



Pressure o'o5i mnii., 67 M, the current of 3,600 cells 

 passed intermittently ; 4,806 cells, C. o'ooigi W, produced 

 a continuous illumination from the positive to within 3 

 inches of the' negative, the discharge at the negative 

 licking the inside of the tube. 



Pressure o'oi mm., 13 M, the current of 4,800 rod cells 

 just passed : with 6,960 cells the current produced no 



appreciable deflection of our galvanometer which would 

 indicate O'ooo24 W- The strata thickened and became 

 much wider. The discharg;e at the negative licked the 

 side of the tube and was very sensitire to the approach 

 of the finger. , 



By standing 16 hours the pressure had somewhat in- 

 creased without leakage having occurred, and was 0*037 

 mm., 49 M, 6,960 cells, current less than 0-00024 W ; 

 the discharge was milky white and quite different from 

 anything before seen by us with a hydrogen residual charge. 

 The strata had become still broader, the negative dis- 

 charge hugging the tube and being very sensitive to the 

 finger. The C and F lines could not be seen with the 

 spectroscope, but there was a double green line near b. 



A charge of hydrogen was let in, the charge being 

 0-001725 of the capacity of the tube and pump, and 

 increased the pressure to 1-311 mm., 1,725 M. 3)6oo rod 

 cells produced a stratification composed of umbrella- 

 shaped strata, united in the middle of the tube by a 

 luminosity one-third the length of the tube. The double 

 green line near b had disappeared, and the C, F, and G 

 lines were visible in the spectroscope. 



Another calibrated charge of hydrogen was let in and 

 raised the pressure to 2-622 mm., 3,550 M; the current 

 of 3,600 cells just passed : with 4^,800 cells a phase was 

 produced resembling tube 129, Fig. 7 in the Plate. 



Another 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 lilies 

 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^'y inch in diameter, baviilig 

 at one end a bulb 2 inches in diameter, from whifch 

 project at right angles to the main tube two short lengths 

 of tube i\ 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 ^^g inch in diameter screwed on to a 

 wire of platinum, and in the head of the T a brass wire, 

 4| 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. 2,400 cells gave a current 0-02289 W) the straight 

 wire being positive, and the cross wire in the bulb 



TUBE 161 



«;< ( < i {<{ (({((iimsiimmmmiw^^^ 



^^yyyy yyy yyyyy y^^Mm^Mwwwm^^^ 



Fig. 17. 



negative; there were produced beautiful double strata 

 intensely blue, completely filling the tube. Strips of paper 

 were fastened over these strata in the region of the stains ; 

 these were found to occupy the unstained spaces; the 

 stains therefore marked the intervals, or cooler parts, 

 between former strata. 



Tube 161, //ydro^en.~The difference of the stt'ata in 

 tubes of different diameter at the same pressure arid with 

 the same current is very clearly brought out in (nTJ6, i6r, 

 composed of two portions, one being 18 inches Idfig' and 

 1-65 inch internal diameter, the other 17-5 inches long, 

 and 0-975 inch diameter, the ratio of the sectional 3*^^33 



being 2-864 to i. The terminal in the small tube is a 

 point, in the large one a ring. 



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 



