Sir W. Harris on some new Phenomena of Residuary Charge. 491 



coating such as he describes was sufficient. It is, however, shown 

 in this paper that the cases of the two jars are widely different. As 

 the spread of the electricity becomes satisfied, a less charge is re- 

 quired for explosion, and the tension of a given quantity increases. 

 The following are the results of experiments with 100 measures 

 similar to the preceding : — ■ 



Full coating. 



Exploding distance '15 Intensity 100° at 1 inch. 



Residual measures 2*45 Therm, electric effect 8°. 



Partial coating. 

 Mean exploding distance .. "25 Intensity 160°. 

 Residual measures 4*97 Therm, electric effect 3°*5. 



It is evident the two forms of coating are not equally efficient, the 

 heating effect of discharge not being half as great in the partially 

 coated jar, whilst the residual charge is twice as great. The experiment 

 so far shows the spread of electricity on the uncoated glass to be a 

 source of absorption of charge to a greater or less extent, and goes 

 far to confirm the views of Mr. Cavendish, relative to the spreading 

 of electricity on glass. 



The phenomena of metal-coated jars having been so far examined, 

 a similar course of experiment is followed with jars coated with less 

 perfect conductors, commencing with water coatings. For this pur- 

 pose a jar exposing nearly 5 square feet of coating was prepared with 

 metal coating, and the results of a charge of 100 measures determined 

 and noted as before ; the metal coating being removed, the same jar 

 had an equal extent of water applied to its opposite surface coating. 

 The method of effecting this is described. The author states that it 

 was so perfect as to shield the experiment from all interference of 

 vapour from the water surface, so that the jar completely retained 

 the charge without any dissipation, and in no sense differed in this 

 respect from a metal-coated jar. 



The results of this experiment are not a little remarkable. The 

 exploding distance of the 1 00 measures, whether with the metal or 

 with the water coating, did not materially differ, except in apparent 

 force, being for the metal *22, for the water *2. The exploding 

 spark from the water coating, instead of the sharp ringing sound 

 attendant on the exploding spark from the metal coating, is weak and 

 subdued, and is often like the sound of fired damp gunpowder. The 

 intensity or attractive force is also in each case alike, or very nearly ; 

 being for the metal coating 144°, for the water 142°. The residuary 

 charges differed considerably, being for the -metal coating about 2'25 

 measures, or about -^th part of the total charge ; for the water 

 coating 14 -5 measures, or about the ith of the total charge. The 

 residuary charge with a water coating is more than six times as great as 

 with a metal coating. The thermo-electric effect with the metal 

 coating was 10°, with the water coating nothing; 200 measures, or 

 double the charge, had no effect on the thermo-electrometer. 



In this experiment it does not appear requisite that both the 

 coatings should be water ; one coating may be metal, as in the first 



