SUBMARINE TELEGRAPHY.] UNDULATOEY FORCE P. ELECTRO-MAGNETISM. 



263 



annoyance of the operators on a line of telegraph ; but 

 euch are not of general interest ; and we shall, therefore, 

 omit to notice them. 



With respect to the various uses to which the electric 

 telegraph is ordinarily applied, it would be impossible for 

 us to enter. Confining our attention to the operations 

 of the companies working the instrument on land, we may 

 observe, that there is no event occurring in daily life 

 which is not constantly made the subject of a message. 

 Politically, commercially, and socially, the electric tele- 

 graph has become an institution of the age. So great 

 has been its development, that, at the present time, all 

 London is intersected with underground wires, and the 

 roofs of the houses passed over by those suspended on 

 poles, for the purpose of accommodating the universal 

 desire for speedy transmission of messages. Nearly every 

 line of railway has its public and private telegraphic 

 arrangements. Warehouses, in different parts of the 

 metropolis and other cities, and the various parts of 

 warehouses and other large buildings, are connected 

 together by electric wires. A company has lately been 

 formed for the purpose of supplying instruments and 

 wire communication between any two or more private 

 establishments in London. Indeed, we may sum up our 

 remarks on this point by stating, that electricity is as 

 effectually "laid on" in most of our large cities in Great 

 Britain, as are gas and water ; although its uses and ad- 

 vantages are not so largely availed of. or required, as 

 uther articles we have named. 



SUBMARINE TELEGRAPHY. 



AFTKR it had been proved that communication could be 

 satisfactorily and readily employed between any two or 

 mure points on land, it was but natural that an attempt 

 should be made to connect countries separated by seas, 

 <tc. , so that electric telegraphic messages might be 

 dispatched from one to another. Of course, the diffi- 

 culty of carrying out the idea chiefly rested in that of 

 insulating the wire, and of giving it sufficient strength 

 to resist all the accidents to which it might be subjected. 

 The first obstacle that respecting insulation was over- 

 come by using gutta-percha as an external coating to 

 the wire ; and the latter was conquered, in most in- 

 stances, by the exercise of that mechanical ingenuity 

 for which this country is generally so greatly renowned. 

 We shall proceed to detail the various results which 

 have been obtained in this interesting branch of electro- 

 magnetic application, and so enable onr readers to esti- 

 mate and understand the triumph which science and 

 skilled labour have accomplished, in this respect, during 

 the last few years. For the purpose of making this 

 subject as clear as possible to our readers, we shall divide 

 it into three parts. Having no reference to the instru- 

 ments which may be used to indicate the message, we 

 shall chiefly confine our attention to the cable, which 

 is, of course, the specialty of submarine telegraphy. We 

 shall consider 



1. The construction of the cable. 



2. Its submersion in the sea or rivers, etc. 



3. The circumstances which interfere with its constant 

 and successful working. 



1. THE CoxsTHUcTiojf OF THE CABLE. A submarine 

 cable requires that it should be sufficiently protected 

 Fig. 28. 



A, 



the iron wiret surrounding the cable ; B, the tarred rope surrounding the gutta- 

 percha covered wires ; C, the gutta-percha covering the wires ; D, the four wires through 

 vi hich the message is sent ; E, an end view of the covering of iron wire F an end view 

 of tte gutta-percha covering, and of the conducting wires. 



hard or pointed substance after submersion ; that it 

 should have strength enough to resist the great tension 

 it undergoes during submersion; and that the con- 

 ducting wire should be so covered as to entirely insulate 

 the current which passes by it, that such may not be 

 diverted from its intended course. These points are 

 secured in various ways, which will be better understood 

 by the foregoing engraving, which is an illustration of 

 the cable laid between Dover and Calais. 



In Fig. 28, we observe, that the outer portion of tho 

 cable consists of a coating of thick iron wires. These are 

 twisted on by means of powerful machinery ; and when 

 this is well performed, they afford a sufficient protection to 

 all that they enclose within their folds. The size of these 

 wires varies according to the strength required, and the 

 circumstances in which the cable may be placed. In 

 shallow water, the external coat requires to be much 

 stronger than in deep sea, because of the pebbles and 

 broken rock against which it may rub. After a cable 

 has laid for some time beneath tho surface of sea- 

 water, it acquires a curious coating, which has the power 

 of affording it additional protection. This consists of 

 the shells of small fish which attach themselves to it. It 

 gradually increases, and sand, <tc., soon become com- 

 pletely attached to the wires, forming an external sur- 

 face of great solidity and strength. This, which, at 

 first sight, seems to be a source of danger to a cable, 

 becomes one of its most valuable protectors ; and, in- 

 stead of decreasing and wearing away, it accumulates 

 continually. Tho dangers, then, of injury from such 

 sources, peculiar to immersion in sea-water, occur only 

 for some time after the cable has been laid, and decrease 

 as the coating we have described accumulates. Wo 

 observe, in Fig. 28, next to the external metallic coating, 

 a covering of hemp, which is wound round the next 

 coating of gutta-percha, enclosing the wire. The object 

 of this coat is to allow of play between the covering of 

 the conducting wires and that which forms the outside 

 of the cable. The hemp is saturated with a mixture of 

 grease and pitch, which, to some extent, tends to protect 

 the gutta-percha from the attacks of marine insects ; for 

 any greasy substance is always avoided by them. 

 Should the cable bo accidentally bent at too acute an 

 angle, the coat, by its elasticity, prevents the snapping 

 of the fine internal wires. 



We next observe a gutta-percha coat, which is, per- 

 haps, the most essential of the throe ; for, being a non- 

 conductor, it insulates the conducting wires which it 

 encloses. When more than one wire is employed and 

 this, with few exceptions, is .always the casu each wire 

 is individually coated with gutta-percha ; and thus the 

 insulation of the entire number is more effectually 

 arrived at. Much of the success which has been ob- 

 tained in the use of submarine cables, is due to tho 

 application of gutta-percha : and the chief manufacture 

 of tho material, and its application to telegraphic pur- 

 poses, is conducted by the Gutta-Percha Company, of 

 Wharf-road, City-road, London ; which has expended a 

 large capital in perfecting this branch of the business. 

 Whilst mentioning names of manufacturers, we must also 

 include Messrs. Newall, of Newcastle-on-Tyne, and 

 M. xrs. Glasse and Elliot, of London, as those who 

 have individually or collectively had the manufacture of 

 all the cables which have been laid round our coasts. 

 From late experiments more especially since tho 

 failure of tho Atlantic telegraph, of which 

 we shall presently speak more fully tho 

 opinion has gained ground, that gutta- 

 percha is not so good an insulator as is to 

 be desired. In fact, tho process of its 

 ^manufacture is such as to introduce chances 

 of failure by the porosity of individual 

 portions. Attention has therefore been di- 

 rected to other materials. Amongst thes- 

 is india-rubber, which has lately been highly 

 recommended as a substitute for gutta- 

 percha, for its insulating and non-porous 



character. Each material has its advocates , 

 from any chance of injury by being rubbed against any | and extended trials are still required to afford accurate 



