470 



NATURE 



[April IS, 1875 



THE PROGRESS OF THE TELEGRAPH* 

 III. 



WHENEVER the finger of scientific research points 

 the way to mechanical applications, the creative 

 powers of the human brain originate a multitude of inven- 

 tions. Too often, however, like the rank growth of weeds 

 which spring up to choke the produce of the soil, they sur- 

 round as parasites the principles involved, and by misap- 

 plied talent, frustrate the simplicity and vigour of the 

 original idea. By hundreds in all forms and shapes have 

 telegraphic inventions crowded into the field ; but ninety- 

 nine out of every hundred patented inventions are not worth 

 even the fees paid to Government. As with the multitude of 

 steam-boiler patents, so with telegraph patents, a very 

 limited number of the different patented inventions have 

 survived to render any really practical aid to the every- 

 day requirements of telegraphic transmissions by land or 

 by sea on a large scale. All the earlier inventions, the 

 five needle, double needle, and the single needle telegraph, 

 Bain's chemical printer, the mechanical alphabetical 

 printer, Morse transmitter, and others of a similar type, 

 have long since been laid on the shelf as incompetent as 

 regards submarine cable transmissions over e.xtended 

 lengths ; and a form of apparatus, more or less derived 

 from a skilful combination of old principles and appliances, 

 have taken their place for practical utility. These instru- 

 ments, to which the descriptions in the present instance 

 will be confined, may be classified into two distinct groups, 

 namely, "recording "and "non-recording "instruments ; or 

 those which mechanically record the signals on paper, and 

 those which are read by the eye or ear, the signals after- 

 wards being registered by hand. Before proceeding to 

 investigate the combinations of principles employed, it is 

 desirable to point out that these several classes of in- 

 strument have each a special department for which they 

 are specially adapted. Thus, for submarine cable trans- 

 missions the non-recording apparatus, depending upon the 

 correctness of the eye or the ear, must at all times be liable 

 to error, the accuracy and precision of sight and hearing 

 of the reader being the only voucher that the trans- 

 mitter of the message has that it has been faithfully 

 interpreted at the distant station. Mistakes under this 

 system must therefore, of necessity, frequently arise. In- 

 struments of the recording type are, in consequence, always 

 to be preferred. 



In all these various forms of apparatus no new principles 

 have been discovered ; they are simply successful mecha- 

 nical arrangements and combinations of certain well- 

 known electrical laws, producing new and useful results. 

 These fundamental principles may generally be described 

 as follows : — 



When a length of insulated wire is wound round a 



Flc. 14.— Horse-shoe electro-magnet, with arm.iture 



piece of soft iron, and an electric current is passed through 

 the wire helix so wound round the soft iron core (Fig. 14), 

 the soft iron becomes a magnet and remains so, so long as 

 the current flows through the wire ; when the current ceases, 

 the soft iron is no longer a magnet ; the polarity of this 

 magnet is reversed according to the direction in which 



* Contuiued from p. 452. 



the current is sent through the coil or the direction in 

 which the wire is wound round the soft iron core. 



When a coil of wire surrounding a soft iron core is 

 passed before the pole of a permanent-magnet, at the 

 moment of passing it becomes a magnet by induction, 

 and at the instant of making and breaking contact with 

 the pole of the permanent-magtiet, a wave of magneto- 

 electricity is induced in the coil of wire surrounding the 

 soft iron core. The current induced at the breaking is in 

 an opposite direction and stronger than the current 

 induced at the making contact. The more rapid and 

 decided the make and break, the stronger the magneto- 

 currents induced in the coil. 



A magneto-machine of this description is shown in 

 Fig. 15. It consists of a powerful permanent magnet, 

 A, E, composed of steel plates in the form of a horse-shoe, 

 firmly fi.xed in a vertical position to a wooden frame, the 

 two poles of the magnet being opposite to two coils of 

 insulated wire, each furnished with a soft iron core. 

 These two soft iron cores are connected together by an 

 iron plate, t, f ; the coils thus arranged constitute an 

 electro-magnet. The electro-magnet thus formed is fixed 

 so as to revolve round an axis, /, which passes between 

 the poles of the magnet, and is connected with an endless 

 chain and wheel with a handle. 



When the coils are put in motion, induced currents of 

 magneto-electricity are developed in each of them, at 

 each successive make and break of the soft iron cores 

 with the poles of the magnet A, B. If the wires of the 

 coils are wound in contrary directions, the induced cur- 

 rents developed in each coil by the approach of the two 

 contrary poles of the magnet will be in the same direction. 



When insulated wire helices are placed round the two 

 poles of a permanent-magnet, so that a continuous circuit 

 is formed, and an'^armature of soft iron is rotated before 

 them, at the moments of the make and break of the 

 revolving armature with the poles of the magnet, a wave 

 of magneto-electricity is induced in the wire helices, the 

 stronger current being that produced by the breaking con- 

 tact, which is in an opposite direction to the weaker 

 current induced in the helices at the moment of making 

 contact. 



