402 Prof. Dr. Jacobi on the Galvanic Spark. 



ments at Konigsberg, and found them confirmed in a very stri- 

 king way if quicksilver was employed in completing the cir- 

 cuit. However the closing spark appeared to me even at that 

 time doubtful, and in contradiction to many other experiments; 

 first because the free electrical tension at the poles of the vol- 

 taic battery, and especially of a single circuit, is too weak to 

 be able to break through a stratum of air ; and then, when the 

 spark has once passed, no reason exists why this should not 

 take place in continuance ; in other words, a continual spark 

 must originate when the distance of the points remains the 

 same. By the subsequent explanation of Faraday, this subject 

 is perfectly settled ; however, in the Repertorium der Physilc, 

 edited by Professors Dove and Moser, both in the first and 

 second part (I. p. 190. II. p. 113.) the closing spark is still 

 represented as something actual, and discussed as such. In 

 the same work, p. 190, several other experiments are enume- 

 rated, in order to show, in the contractions of the frog, phse- 

 nomena analogous to the closing spark. These experiments, 

 however, are too much confused to be of any importance with 

 respect to the subject in question or any other. It is further 

 stated as a remarkable difference, that the smaller the con- 

 necting wire between the exciting plates, the stronger is the 

 spark at closing, and the more insignificant at breaking con- 

 tact. This singularity is also reduced to a normal phaeno- 

 menon by Faraday's explanation, as the phsenomena of 

 combustion are always more intense when there is less oppo- 

 sition to conduction ; therefore a shorter wire in the circuit 

 has the effect in question. Finally, one can scarcely consider 

 the arrangement given by Linari. for the production of a 

 thermo-magnetic spark as an apparatus which, as is the case 

 in the above-mentioned work, ii. p. 113, can be employed to 

 decide this point, so important for the theory, but yet so intri- 

 cate, whether in reality a spark can take place previously to 

 contact. 



It appeared to me more fit, since in the end all depends on 

 a positive determination, to fix to a beam-compass {Stangen- 

 zirkeT) with a micrometer screw two very finely pointed 

 wires, which in this way might be very accurately and gra- 

 dually approximated to each other. Their distance and the 

 other phsenomena were measured and observed with a micro- 

 scope with micrometrical apparatus. For the latter I am 

 obliged to the kindness of M. Lenz, who was also so good as 

 to witness the experiment. I employed a battery of zinc and 

 platina consisting of 12 plates, each of 24? English square 

 inches surface, which might also be connected into a single 

 pair of plates by means of a 2' square surface of platina. The 



