248 ELECTRO-TELEGRAPHY 



magnetism entirely from his marine galvanometer by surrounding it with a heavy 

 armour of soft iron, which gives it the advantage of retaining its constant of sensibility 

 and zero point in whatever position the ship's head may bo put ; ho also keeps his 

 mirror magnet steady by suspending it to a tightly-drawn cocoon fibre. 



1 The measuring ^apparatus on board does not materially differ from that used on 

 shore, only, whore it is possible, it is made simpler. On the sea everything is damp, 

 and with a dampness caused by the particles of salt water carried by the wind ; these 

 particles of water are conductors, and provide a short circuit for the current to earth 

 from every corner of the apparatus. Therefore, the fewer the pieces used, the fewer 

 the chances are that the " subtle fluid " departs from the way it should go. 



' Before commencing to pay out a cable, and while the ship is quiet in harbour, 

 careful measurements are made of its insulation, copper resistance, and temperature. 



' In commencing to pay-out a cable, one end of the shore-cable is put upon the land 

 and carried into the station. The ship pays this out to the end, when it is joined to 

 the middle-cable, or to the deep-sea-cable if no middle-cable is employed. At this 

 point, the officer of the ship takes the bearings carefully in his nautical way, and the 

 telegraph engineer takes his bearings in a less scientific and much simpler way. These 

 consist in rough sketches of marked points on the coast. The line which a church 

 makes with a hill, or two hills together, or an inlet with a hill behind should bo care- 

 fully noted. There are very few coasts which do not present such inequalities as to 

 enable the engineer to find lines between distant objects. Of these lines two at least 

 should bo noted, if possible making an angle of 90 with each other; and the objects 

 noticed on the land should be, one as near to the water and the other as far from it as 

 the nature of the coast permits. In the long run, this method is the most valuable, 

 and enables the engineer to return at any time to the exact locality of the point, in 

 case he may want to pick it up. 



' From this point begins the most difficult and risky part of submarine telegraphy. 

 The manufacture requires a constant supervision and care ; it has, however, the advan- 

 tages of terra-firma, and any accident may be repaired, because the essential element 

 time, is to bo had ; but the laying demands untiring courage and caution, and that, 

 because when once under way, there is no stopping without danger to the cable, not- 

 withstanding the innumerable casualties which invariably attend a sea voyage.' 



In his new book on telegraphy (' Trait6 sur lo Telegraphic') M. du Moncet says 

 that in order to lay a cable successfully the speed of the ship should be precisely that 

 of tho outlying cable. Unfortunately for the telegraph engineer, this physicist's ideas 

 of the sea bottom do not correspond with the reality. Instead of being level like a 

 street, it is found that as great irregularities occur in the earth under the water, as in 

 the earth above it. The sea has its mountains, its valleys, its precipices, as well as 

 the dry land, and over these mountains, and across these valleys, and up and down 

 these precipices, the cable must be laid, and not hung from peak to peak like a tight 

 rope. It must everywhere rest upon the bottom ; if not, it must sooner or later break 

 by its own weight between the points of suspension, or abrade against tho rocks until 

 it is cut through.' 



The following conclusions appear to have been arrived at by those connected with 

 the working of the Atlantic electric cable : 1st, That an insulated submarine wire 

 conducts according to a different law to that of a circuit suspended in air ; 2nd, That 

 the rate at which a voltaic signal travels along a wire is not affected by the intensity 

 of the battery ; and 3rd, that magneto-electric induced currents have tho property of 

 travelling much faster than voltaic ones, and increase in tho rapidity of travelling, 

 when their intensity is increased. Mr. Samuel Alfred Varley, in a paper read before 

 the Institution of Civil Engineers, makes the following remarks on those points : 



' In examining those conclusions, it has first to bo considered whether tho conditions 

 of a submarine circuit and of a suspended one are different. In a suspended wire, tho 

 insulating medium of the air takes tho place of tho gutta-percha of the submarine 

 circuit. The earth, which is tho nearest conductor, is a considerable distance off, and 

 is only on one side of tho wire ; therefore, but little induction can take place between 

 the wire and tho earth. Nevertheless, induction to a certain extent does take place, 

 and can be perceived in circuits of very moderate length. The author has noticed 

 indications of it in a circuit 60 miles long, and ho feels confident that, with delicate 

 apparatus, it could bo perceived in much shorter circuits. If tho distance between tho 

 wire and tho earth is decreased, induction will bo developed more strongly, and the 

 wire could be brought down, step by stop, until tho condition of a submarine circuit 

 would bo approached, where the earth surrounds the wire on all sides, and is only 

 separated from it by the thickness of th or ^jths of an inch of gutta-percha, a substance 

 possessing, moreover, specifically a much greater inductive capacity than air. It 

 therefore appears that the conditions are precisely tho same, only differing in degree. 



In a Leyden jar, the inner and outer coatings are perfectly insulated ono from tho 



