XI. APPLICATIONS. 349 



The great risk the parties ran can be better appreciated from the fact that 

 three successive attempts by other parties to establish submarine cables 

 between England and Ireland occurred soon afterwards, which all failed. 



The above-named gentlemen were also instrumental in laying the next 

 successful cable between Dover and Ostend. 



This latter was constructed in a similar manner to the original one, and 

 they are both still in operation. 



No fundamental change has yet been effected in the form and mode of 

 construction of heavy cables, thus proving satisfactorily that the first type of 

 heavy submarine cable laid upwards of twenty-five years ago is practically 

 right in principle. 



1508f. Magneto-Electric Machine termed a * Thunder 

 Pump." Reid Bros. 



15O8g. Cooke and Wheatstone's Coil, 1837, with front 

 and back needle ; coil wound with cotton covered wire. 



Reid Bros. 



15O8h. Reid's Patent Circular Coil, 1848, with front 

 and back needle complete ; coil wound with cotton covered wire. 



Reid Bros. 



146. First Instrument for recording Signals through 



Long Submarine Cables, by curve 01 perforations produced by- 

 sparks from a Ruhrnkorff coil guided by a platinum wire moved 

 by a needle under the influence of the varying current from the 

 cable. Sir William Thomson. 



SPECIAL COLLECTIONS ILLUSTRATING THE HISTORY OF ELECTRIC 

 TELEGRAPHY, CONTRIBUTED BY H.M. POSTMASTER GENERAL. 



1508e. Cooke and Wheatstone's Earliest Needle Tele- 

 graph, 1837. 



The letters are indicated by the convergence of two needles. The five line- 

 wires required for the instrument were inserted in grooves in a triangular piece 

 of wood, and wire laid underground. 



1509. Cooke and Wheatstone's Four-Needle Telegraph, 



1838. 



Some of the letters are indicated by the convergence of two needles, as in 

 the five-needle instrument, the rest by one or more movements of the needles 

 to the right or left. . 



1548. Cooke and Wheatstone's Revolving Disc Tele- 

 graph, 1840. 



A step-by-step instrument. The letters of the alphabet are arranged round a 

 paper disc fixed on the axle of an escapement wheel. 



The letters are presented at an opening in the front of the case. 



The escapement is similar to the " echappemeut-a-cheville," and is con- 

 trolled by an electro-magnet. 



