20 Journal of the Asiatic Society of Bengal. [N.S., XVI, 
Protected insulator. No desiccant used. 
Time after ex- . 
posure to dir. Ebonite. Amber. Paraffin. 
0 0067 ya | ‘0075 
15 hours 014 AE: “008 
18 a ri “009 
20 sie ‘013 O17 
35 0090 “015 Se 
50 oy “014 
65 is | 023 
Same insulators. Sulphuric acid drying. 
Initial 0:0090 0-013 0:017 
Immediately after. 0-0038 0:0097 as 
ay ia 0:0087 
00064 0:0079 Sa 
10 0-015 a 0-020 
165s: ce 0:0097 ie 
ur, thus serving as a guard ring. By 
means of a connection soldered to a small projection P on the 
outer rim of the guard cylinder this can be charged to any po- 
tential either positive or negative. The diameter of the sul- 
Pp aehhaaialaantaritaiek ga 
| LLL LLL 
PEL LLL 
Mm 
i lateatlhahh hhh dh db tdi 
phur plug is reduced to about 12 mm., that of the cylinder 
being 8 mm. The external and internal surfaces of the 
sulphur plug, as well as the ends of the brass cylinder, are 
made flush with the corresponding surfaces of the case itself. 
The object of this is partly to reduce surface creep of electrifica- 
tion over the insulator, and partly to prevent dust from collect- 
ing on the surfaces exposed to the outer air. By applying to 
the guard cylinder a potential exactly equal to that of the wire 
passing through the sulphur plug, the effect of any leakage 
