of Danger in Torpedo Experiments. 79 



water off' the "Williamstown Railway Pier. With the same 

 metals, therefore, the electromotive force of the cell would be 

 less at Williamstown than it would be at Queenscliff. 



I would invite your attention to the differences in the fuses 

 used. They are supposed, and certainly were intended, to 

 be uniform, and yet we find them to vary greatly in point 

 of sensitiveness; and this naturally leads me to repeat the 

 remark that some degree of uncertainty attaches to the 

 constants that enter into calculations like the present. Thus, 

 I have had to use two values for the electromotive force of 

 the cell, of which values both cannot, and neither may be, 

 correct, for the true value may lie between the two. These 

 two values, as well as the other constants I have made use 

 of, must be regarded as the mean or average values, resulting 

 from a number of measurements. Hence, a current that 

 will explode one fuse will fail to explode another supposed to 

 be similar ; and if theory shows that a certain kind of fuse 

 should explode through a certain length of wire, one fuse 

 may explode through a greater while another may fail to 

 explode through a less length. 



Thus the foregoing calculations point to a doubtful and 

 dangerous region between the positively will and the posi- 

 tively will not, a region in which a fuse may or may not 

 explode, according to circumstances not fully known to us, 

 and which, therefore, cannot enter into our calculations ; and 

 if it be an object to avoid an explosion, we should make it 

 a point to keep as far from this region as practicable. 



This is fully recognised in the instructions for guidance in 

 torpedo operations. If it be an object to make an explosion 

 certain, it is usual to provide a current double that which 

 theory shows to be just sufficient. If, on the other hand, 

 it is necessary to send a current through a fuse without 

 exploding it, as in certain testing operations, which I need 

 not particularise, it is important that the current should be 

 so small as to preclude danger of an explosion. And as 

 bearing on the subject of the late accident, it is of interest 

 to note what is considered as the limit of danger. The 

 Submarine Mining Drill Booh forbids the use of a larger 

 current for testing than *S Veber ; any current exceeding 

 that, is presumed to be more or less dangerous. A sea-cell 

 current between the hull of an iron vessel and a large zinc 

 plate through the wire used at Queenscliff and a No. 12 fuse 

 would be from *5 to '55 Veber. 



H 



