200 Proceedings of Royal Society of Edinburgh. [sess. 
Society on 30th January 1893, and he found, if rightly reported, 
that when the hearing wire was floating he got results, hut when 
it was allowed to descend that no observations could he got ; he 
attributes this to reflection from the surface of the water ; this, 
however, is unlikely, as the reason that no sounds were then heard 
was that the major part of the wire lay on an equipotential line. 
Electro-magnetic waves enter or leave salt water practically unim- 
paired, as the following diagram (fig. 5) will show, where A is a 
wire suspended 10 feet above salt water and B is a wire sunk in 
salt water. On trial, it was found, as stated in my paper read 
before this Society in January 1893, that there was no practical 
difi“erence in air or salt water to the propagation of electro-magnetic 
waves, in or out the distance to which waves went, the distance 
to which the currents could be heard being immaterial whether the 
detector was sunk or in air. 
It has been attempted to be shown that the coil system is not only 
theoretically but practically the best. Meantime, my brother has 
recommended the Commissioners of l!^’orthern Lighthouses to erect 
the coil system at Muckle Flugga, and the Commissioners have 
approved, and I hope that we may soon hear of this novel system 
of communication being erected at the most northern point of the 
British Isles, where the laying down and after-maintenance of a sub- 
marine cable is practically impossible. This system is also applicable 
to our warships, to assist in their manoeuvring, by the establishment 
of instantaneous communication unaffected by wind or weather. 
The application of the coil system to communication with light- 
vessels is obvious, namely, to moor the vessel in the ordinary way, 
and lay out from the shore a cable, and circle the area over ’which 
the lightship moorings will permit her to travel by a coil of the cable 
the required diameter, which will be twice the length of her chain 
cable. On board the vessel there will be another coil of a number of 
turns of thick wire. Ten cells on the lightship and ten on the shore 
will be sufficient for the installation. The system erected at Kentish 
Knock and other light-vessels is expensive in moorings, and is liable 
to derangement, and requires special appliances; whereas, by the 
coil system there can be no derangement, and the vessel can be 
moored in the ordinary way. A call arrangement and telephones 
complete the installation. 
