226 POPULAR LECTURES AND ADDRESSES. 



\Yhcn arrangements can be made for simul- 

 taneous observations of the potentials by an electro- 

 meter at the two ends of the line, the results will 

 be still more valuable. And, lastly, I may just 

 say that when an electrometer is not available, a 

 galvanometer of very large resistance may be 

 employed. This will not in the slightest degree 

 interfere with the practical working any more than 

 would an electrometer, nor will it be more difficult 

 In get results of the scientific observations not 

 overpoweringly disturbed by the practical working 

 if a galvanometer is used than when an electro- 

 meter is available. The more resistance that can 

 be put in between the cable and the earth in circuit 

 with a galvanometer the better, and the sensibility 

 of the galvanometer will still be found perhaps 

 more than necessary. Then, instead of reducing 

 it by a shunt, let steel magnets giving a more 

 powerful direction to the needle be applied for 

 adjusting it. The resistance in circuit with the 

 galvanometer between cable-end and earth ought 

 to In- at least twenty times the cable's copper- 

 resistance to make the galvanometer observations 



