.S7A' WILLIAM SlEMt:.\S, /:A'..S. 127 



the instrument could be applied. Moreover, by the adoption of re- 

 sistance-boxes a great deal of the difficulty \\hich Professor Foster 

 had met with was avoided, because the stopper made a very safe 

 contact. Moreover, the wire with sliding contact was apt to wear 

 if much used, and the resistances of comparison consisted of 

 fractions of units only, whereas the resistances to be measured 

 amounted usually to hundreds, thousands, hundreds of thousands, 

 and millions ; it also followed from this condition that a galva- 

 nometer of exceedingly small resistance must be used, in order 

 to get a proper proportion between those resistances, to give a 

 maximum effect ; whereas with box-resistances, they could use a 

 galvanometer of many thousand units in its point of maximum 

 sensitiveness. He would ask Professor Foster to be good enough 

 to state whether he had compared his improved instrument which 

 appeared to be very ingenious as a method of avoiding errors in 

 dealing with small resistances whether he had compared that with 

 the instrument with the resistance-boxes ? 



In the discussion of the Paper 



"ON ELECTRICAL IGNITION OF EXPLOSIVES," 

 By MAJOR STOTHERD, 



THE PRESIDENT* (Mr. C. W. Siemens), in closing the discussion 

 said the subject was of very great interest, which had partly occu- 

 pied his attention for a long period. Members might not be aware 

 that the first application of torpedoes and submarine mines was 

 made as early as 1848, in the harbour of Kiel. The torpedoes 

 consisted of bags of gunpowder connected with batteries on 

 land by wires insulated with gutta-percha. He believed that 

 was the first application to this purpose of insulated wires. 

 These mines were to be exploded when a ship came over them, 

 and the position of the ship was determined by a reflector. In the 

 latter period of the Austrian war, a great number of torpedoes were 



* Excerpt Journal of the Society of Telegraph Engineers, Vol. I. 1872-73, 

 p. 223. 



