ELECTRICAL SCIENCE. 167 



Professor Hughes has produced a Dial Electric Telegraph, consist- 

 ing of a train of wheels set in motion by a spring, and governed in its 

 revolution by means of a vibrating spring. The dial revolves by 

 means of friction, and whenever the keys upon which the letters of 

 the alphabet are engraved are pressed down, the wheel is stopped 

 and the electric circuit is closed. This attracts an armature of an 

 electro- magnet at the distant instrument, which stops the dial by 

 means of a catch ; thus the distant instrument imitates what is done 

 upon the transmitting one. Any person can work this instrument 

 without possessing any previous knowledge of such matters. 



Among the improvements in The Insulation of Electric Telegraph 

 Conductors is one by Mr. F. N. Gisborne, and is for suspended line 

 wires. Mr. Gisborne's insulator consists of an enamelled cast-iron 

 cap, with an enamelled wrought-iron screw-pin ; the interior of the 

 cap being of a globular form, affords protection against the admission 

 or accumulation of moisture. This insulator holds the main wire, 

 upon a broad basis, without the assistance of any tie-wire or other 

 fastening, and in such a manner that it cannot draw or slip ; each 

 pole therefore sustains its own legitimate amount of weight and 

 strain. It is readily attached to a pole or wall without anj r additional 

 fastenings, and when attached remains perfectly firm in every par- 

 ticular. 



Neit Instruments. — Mr. Thomas Allan, C.E., to whom we pri- 

 marily owe the practical abandonment of heavy wire- bound sub- 

 marine telegraph cables, has embodied these telegraphic improve- 

 ments. The first relates to what are called pole- changers, or relays. 

 A great difficulty with these has hitherto been the derangement 

 caused by the action of the spark upon the delicate contact points 

 ot the relay. Now, this evil Mr. Allan has got rid of altogether, 

 ty combining an improved relay with an improved recording in- 

 strument, in such manner that the spark is not produced in the relay 

 at all, but in the recording instrument, where it is of far less 

 consequence. This improvement is attended by an immense ad- 

 vantage, for, now that the relay is relieved of the spark, the limit 

 which has hitherto been practically placed upon the power of 

 the local battery is removed. Of this fact Mr. Allan has availed 

 himself in a most ingenious manner, by placing induction coils 

 around the electro-magnets of the sending and receiving instru- 

 ments, and so dispensing with the series of cells generally used for 

 line currents, making the one primary current do the double work of 

 recording its message and operating the successive distant relays, 

 throughout the entire circuit. In the new recording instrument, 

 every current makes a sign, as the relay does not require an opposite 

 current to put it in position to print the next mark, as is generally 

 done, nor does it need any spring or weight to bring it to a position 

 in which the local circuit may be cut off; the printing magnet does 

 that. This magnet also draws through the paper on which the mes- 

 sage is to be received while (and only while) the signalling is con- 

 tinued. The new sending instrument, by Mr. Allan, is of a simi- 



