76 On the Sea-cell as a Possible Source 



which resistance = about 48 yards ; and for the higher- 

 Total resistance of circuit ... '752 Ohm 

 Resistance of fuse at 400° F. ... -402 „ 



Resistance of wire ... '350 ,, 



which resistance = about 44J yards. 



Through any length of wire considerably exceeding 48 

 yards, therefore, contact of the wire with the body of the 

 vessel would be comparatively safe. Through all lengths of 

 wire between 48 yards and 44J yards the charge might or 

 might not explode, according to the quality of the gun-cotton. 

 Through lengths less than 44J- yards the charge certainly 

 should explode. 



Bearing in mind that the resistances of the best made 

 wires and fuses will vary as the quality of the metal, the 

 size of the wire, and, in the case of the fuse, as the lengths 

 of the wire vary, it will be apparent that no sane person 

 would for a moment trust his own life or the lives of others 

 to the chance of a charge not exploding through any length 

 of wire at all near the higher of the limits I have given. 



Different results follow from using the more sensitive 

 fuse, No. 13, and bv taking the lower value for the electro- 

 motive force. The results are embodied in the following 



table : — 



Lengths of No. 16 wire between which 

 explosion may be expected. 

 48 yards — 44^ yards 

 65$ „ - 54 „ 

 39 „ — 35|- „ 

 46 „ — 34 „ 

 For lengths exceeding the greater lengths the charge may 

 not be expected to explode ; for lengths shorter than the 

 less the charge should explode. 



In such a circuit as that in question the fuse of itself 

 forms so large a portion of the total resistance of the circuit 

 that a slight variation in its resistance has a very appreciable 

 effect. The resistance of the fuse when cold is equal to that 

 of about 41 j^ards of No. 16 wire. If the bridge of the fuse 

 consisted of *2 inch instead of "3 inch of platinum wire, its 

 resistance would be about *1 Ohm less. Hence, to maintain 

 the same strength of current, an addition of 1 Ohm, or about 

 12 J yards, might be made in the length of the firing line. 

 But as a less current would fire such a fuse, more than 12J 

 yards might be added without decreasing the efficiency of 

 the current. 



Electromotive 



No. of 



Force. 



Fuse 



•564 



12 



•564 



13 



•514 



12 



•514 



13 



