62 THE SCIENTIFIC PAPERS OP 



The British Government, in promoting these enquiries, has 

 stimulated and directed individual efforts, proving that England 

 fully appreciates the advantages of the submarine electric tele- 

 graph, and is determined to realise the same, thus contrasting 

 favourably in this, as in many other cases of practical progress, 

 with other nations. 



APPENDIX. 



No. 1. Resistance of Short Cables. 



One pole of a battery of n elements is joined to the cable while 

 the other pole is to earth ; then, if < represents the angle through 

 which the galvanometer is turned to bring the needle again to 

 zero, the following equation is established : 



nE 



x+ w l 



E representing the electromotive power of one element, x the 

 unknown resistance of the cable, and W^ the resistance of the 

 galvanometer. 



In order to arrive at the actual value of the insulation resist- 

 ances, a known resistance, say of 10,000 units, is introduced 

 into the circuit instead of the cable, the sensibility of the instru- 

 ment weakened (to y^) by a branch resistance, W 2 , and the 

 number of cells reduced to one. Another equation is then 

 obtained, in which I may represent the force of the current in the 

 whole circuit to be 



E and the strength of the current passing 



io,ooo+|^-|? 



'' 1 "f" '' 2 



through the galvanometer will be 



W a .E 1 



= sm <f) l = 



2 10,000 + w ^~ 



