On the effect of Terrestrial Currents on Telegraph Wires. 339 



Experimental Table III. 



Diameter of tube = -18 inch. Lenp:th of the column of liquid, 

 L = 20 inches. 



Here the limiting angle of resistance /8 = 2°, the angle of 

 minimum time of descent ^i = 50°, and the general formula is 



62 

 '^^ sin (2^-10) -f sin 6"^^* * ' * ^^^ 



Precisely the same results as those above given were obtained 

 with the tube closed at its lower extremity, and an air-bubble 

 not less in length than fifteen times the diameter of the tube. 

 With smaller air-bubbles the times of descent of the liquid are 

 sensibly diminished, but in all cases the law relative to the angle 

 of minimum time of descent holds true. 



Hastings, September 9, 1859. 



LI. Method of obviating the effect produced by Cutrents in 

 Telegraph Wires induced by Terrestrial Currents. By H. W. 

 Elphinstone, Esq.* 



AB, CD are two similar telegraph wires, parallel to each 

 other, separated by a small space ; at F they communicate with 

 the two ends of the helix of a galvanometer F ; at E there is a 

 commutator by means of which the two telegraph wires can be 



put in contact with each other, or be joined respectively to the 

 poles of a battery. 



Coinmuuicated by the Author. 



Z2 



