1891.] the Discharge of Ley den Jars. 5 



After a number of readings of spark-length, which have been else- 

 where published (and which showed among other things that it made 

 very little difference whether the alternative path were copper or 

 iron), a common Leyden jar was substituted for the condenser, and 

 similar results were obtained with it. 



But it was now noticed, in addition, that the jar frequently over- 

 flowed by sparking over its lip ; and that when this happened a spark 

 still occurred at B though not at A. 



A special overflow or short-circuiting path was then provided, 

 equivalent to a pair of discharging tongs ; calling this air-gap C, it 

 was found that, according to the adjustment of the width of spark- 

 gaps, flashes at B and C could be got without A ; or at A and B 

 without C ; or at C only. (This was the beginning of experiments on 

 overflow.) 



Putting acid resistance into the circuit at M or at N weakens but 

 does not stop the B sparks ; and it has the same effect at M as at N. 

 But inserting resistance at Q does not weaken the B spark per- 

 ceptibly; neither does cutting the wire there; only of course, in 

 order to permit the charging of the jar in this case, the B gap has to 

 be bridged by some imperfect conductor ; this shunt high resistance, 

 which may be a piece of dry wood or anything just sufficient to 

 convey the charging current, having no appreciable effect upon the 

 B spark. 



But it was noticed that when the wire was cut at Q a singularly 

 long spark or strong brush discharge attempted to jump the space 

 there whenever the machine spark occurred. (This was the beginning 

 of experiments on " recoil- kick.") 



It was also found that connecting the machine side of the jar to 

 earth (the long wire, not interrupted anywhere, being insulated) 

 increased the strength of the B sparks very much, and made them 

 easier to get. Evidently the wire was acting as one coat of a con- 

 denser, the wall being the other coat. Even when the jar was dis- 

 carded, no connexion being made in its place, and the wire alone 

 used, sparks occurred at B perfectly well whenever the machine gave 

 a spark at A. (This led to experiments on " the surging circuit.") 



EXPERIMENTS ON OVERFLOW (February, 1888). 

 Small Jar. 



4. Tried the arrangement shown in fig. 2, the jar being pint size, 

 as described above, of plain cylindrical shape, open at top, with its lip 

 projecting 2 inches above the tinfoil so that the overflow distance was 

 4 inches. The long wire was the 30 yards of No. 1 copper. In addi- 

 tion to the machine spark-gap A, a couple of other intervals labelled 

 D and F were also provided ; the spark-gap D being led up to 



