1892-93,] Mr Stevenson : Induction through Air and Water. 25 
Induction through Air and Water at G-reat Distances 
without the use of Parallel Wires. By Charles A. 
Stevenson, B.Sc., F.B.S.E., M.Inst. C.E. (With a Plate.) 
(Read January 30, 1893.) 
At the beginning of last year I proposed that a cable might be 
laid down in the sea, and, by changing the electric state of the 
cable, that vessels passing near or over it might be able by means of 
a detector on board to discover that they were in its vicinity, and 
hence to locate their position. Some experiments showed that the 
method was feasible, and that water offered no insurmountable 
difficulty ; and having been assured that no known instrument could 
detect the currents that could, with our present machinery, be 
passed through a submarine cable, a series of exhaustive experiments 
were made, with the result that I have constructed two such 
instruments that will act through over 30 fathoms of water, and I 
have been unable to discover their like. 
The first instrument now brought before the Society is a coil of 
uninsulated copper-wire rope, or other water connection, dipping 
into the water at the bow of a boat, and a similar water connection 
at the stern (fig. 1). If these are joined by a wire with a telephone 
on the circuit it will be found that even without an induction coil 
or other arrangement to magnify the effect a very sensitive instru- 
ment is produced, and that when the wires from bow to stern of the 
boat are at right angles, or nearly so, to a cable laid in the water at 
some distance from it, the sounds produced by a magneto-electric 
machine connected to one pole of the machine are audible in the 
telephone. If the water connections are equidistant from the cable, 
as they would be if the boat were immediately over the top of it or 
lying broadside on, no sound is, of course, heard. 
The action takes place when the coils in the water are insulated. 
The cable also may be insulated or uninsulated, as is shown by the 
diagrams (fig. 1), showing effects with different cables, these experi- 
ments being made with a small medical battery 4" in length. The 
action, of course, is similar with an induction coil, and will also act 
if the potential of the cable is changed and is then kept so. In this 
