ELECTRICITY. 



resinous varnish. The liquid should be 

 applied with a flat, camel-hair pencil, 

 the glass being previously warmed. 



On the other hand, it is a curious 

 circumstance, that there is a degree of 

 humidity in the inside of the jar, not 

 only compatible with a high charge, but 

 which even contributes to retain it. 

 This effect was accidentally observed 

 by Mr. Brooke, and afterwards by Mr. 

 Cuthbertson, who states that a jar will 

 take a much greater charge, namely, 

 one- third more, if its inside be consider- 

 ably damped by blowing into it with the 

 mouth through a tube reaching to the 

 bottom. The explanation of this re- 

 markable fact has been given by Pro- 

 fessor Robison on the principles for- 

 merly explained, namely, that there is 

 no electric intensity so great, but that it 

 may be insulated by the least imperfect 

 conductor, provided the latter be long 

 enough, and so constituted as that the 

 intensity of the electricity it contains 

 shall diminish by sufficiently gentle gra- 

 dations. An uniform dampness, in- 

 deed, will not do this ; but it will dimi- 

 nish the abruptness of the variations of 

 intensity, and thus give security against 

 a spontaneous discharge. A similar 

 protection against the breaking of the 

 glass is afforded by placing a layer of 

 paper between the glass and the tin-foil, 

 and making it extend also an inch be- 

 yond the coating. 



(131.) Glass balloons of a spherical 

 shape, being of more uniform thickness 

 than jars, would be much preferable for 

 the construction of an apparatus of this 

 kind, were it possible to apply an uni- 

 form coating to the inside. Professor 

 Robison recommends the following con- 

 struction for a portable jar, which he 

 found to answer exceedingly well. A 

 long-necked phial was made of sheet 

 tin, and then coated entirely on the out- 

 side with line sealing-wax, one thirtieth 

 of an inch thick. The sealing-wax was 

 then coated with tin- foil, all but the 

 neck. It is evident, that the wax here 

 acts the part of the glass in the common 

 *ar, the tin plate corresponding to the 

 inner coating and wire, and the tin-foil 

 to the outer coating. The dissipation 

 is almost nothing if the neck be very 

 small ; and it only requires a little cau- 

 tion to avoid bursting by too high a 

 charge. Even this may be prevented 

 by coating the sealing-wax so near to 

 the end of the neck, that a spontaneous 

 discharge must happen before the accu- 

 mulation is too great, Alternate layers 



of tin- foil and hard varnish form also a 

 very compendious battery. It admits 

 of a surprising accumulation, without 

 shewing any vivid electricity ; but it 

 must be used with more caution, lest it 

 should be spoiled by a spontaneous dis- 

 charge, in which case we cannot disco- 

 ver where the flaw has happened, and 

 the whole is rendered useless. 



(132.) By combining together a suffi- 

 cient number of jars we are able to 

 accumulate an enormous quantity of 

 electricity : for this purpose all the in- 

 terior coatings of the jars must be made 

 to communicate by metallic rods, and a 

 similar union must be established among 

 the exterior coatings. When thus ar- 

 ranged, the whole series may be charg- 

 ed, as if they formed but one jar ; and 

 the whole of the accumulated electricity 

 may be transferred from one system of 

 coatings to the other, by a general and si- 

 multaneous discharge. Such a combina- 

 tion of jars is called an Electrical Battery. 



(133.) It is evident, that an apparatus 

 of this kind, consisting of a great number 

 of parts, must be more liable to derange- 

 ment than a single jar: for if any one 

 of the jars should happen to break by a 

 spontaneous explosion, the whole battery 

 would be rendered useless, until the 

 broken jar be removed. It is prudent, 

 therefore, to secure the adjacent jars 

 from actual contact, by fixing them in a 

 box having thin partitions ; the coated 

 bottoms of the jars resting on a trellis 

 of wire, or on a sheet of tin-foil, which 

 may establish a general communication 

 between them ; while the rods from the 

 interior coatings are connected above by 

 cross wires, having balls at their ex- 

 tremities in order to obviate the dis- 

 sipation of the electricity. On the other 

 hand, by limiting the communications to 

 a certain number of jars, we have it in 

 our power to charge only a part of the 

 battery, without employing the whole. 



CHAPTER IX. 



Management of Electrical Jars and 



Batteries. 



(134.) FOR the purpose of making the 

 direct communication between the inner 

 and outer coating of ajar or battery, by 

 which a discharge is effected, the in- 

 strument shown in fig. 32, and which is 

 Fig. 32. 



