490 Royal Society : — 



very nearly ; intensities and thermo-electric effect of discharge as 

 square of the quantity or number of measure accumulated. 



The author finds that for every metal-coated jar, whether large or 

 small, of thick or thin glass, exposing from 1*5 to 6 feet of coating, 

 the residual charge or quantity left undischarged, varies between the 

 limits of y\jth and -^th of the total charge. 



Experiment 2 investigates the effect of thickness of glass. Two 

 jars, exposing 2*5 square feet of coating, were employed, their rela- 

 tive thickness being as 1:2, that is, -^yths an( i ^y tns °f an m ch ; 

 100 measures were accumulated and discharged at their respective 

 exploding distances. The following results appeared: — exploding 

 distance directly as thickness of glass ; intensity or attractive force in 

 direction of electrometer as square of the thickness ; residuary charge 

 in each case the same, being about ^g-th part of the total charge ; ther- 

 mo-electric effect of discharge very nearly the sa*me ; so that whether 

 discharged from thick glass or thin, under intensities of very different 

 degrees the same quantity of electricity produces the same effect. 

 The intensities in this case were as 4 : 1, yet the thermo-electric effect 

 did not differ more than one or two degrees, one being 1 2°, the other 

 13°. The author finds, by numerous experiments on a series of jars, 

 that the intensity indication has no influence on the force of discharge, 

 the quantity discharged being the same. In a series of jars of dif- 

 ferent magnitudes, and in which the intensity of a given charge of 

 100 measures varied between the limits of 100 and 1000 degrees, 

 there did not appear a difference of more than a few degrees amongst 

 the whole ; the effects varied between 8 and 1 1 degrees. Some little 

 difference will generally arise in favour of electricity accumulated on a 

 small area of coated glass ; in consequence of the greater facility of dis- 

 charge the accumulation has greater freedom of operation through the 

 external circuit, as is shown by its greater effect on the electrometer. 



A celebrated electrician, the late Mr. Brooke of Norwich, in a con- 

 ference with Cuthbertson about the year 1800, stated that a Leyden 

 jar coated with strips of metal j ths of an inch wide, leaving intervals 

 of the same width between the strips, was equally efficient as a full 

 coating in the ordinary way. Two equal and similar jars, about 

 1 foot in diameter and 19 inches high, were prepared accordingly; 

 one fully coated to about 4 square feet, the other coated in strips 

 to about 3*5 square feet. The author, although doubting this state- 

 ment in all its generality, still considered an investigation of it, more 

 especially coming from such men as Brooke and Cuthbertson, desi- 

 rable, and as being calculated to throw further light on the pheno- 

 mena of the Leyden jar. 



A few preliminary experiments seemed to accord with Mr. 

 Brooke's view ; the exploding distance of the two jars with a given 

 charge did not appear extremely different. The accumulated elec- 

 tricity spread upon the glass between the strips of metal, and thus 

 enabled the partially coated jar to receive a larger accumulation, upon 

 the principle stated by Cavendish, than was really due to its extent 

 of actual coating. Mr. Brooke, in the then state of practical electri- 

 city, might have been therefore easily led to imagine that a partial 



