170 ANNUAL OF SCIENTIFIC DISCOVERT. 



of the units of distance travelled. The retardation practically docs in a 

 measure exceed the simple arithmetical ratio of units of distance traversed ; 

 but this departure from the law of the simple series is in all probability due 

 to the retardation caused in the further portions of the conducting wire by 

 the increasingly exhausted condition of the weakened stream. "When the 

 amount of electro motive force is fairly proportioned to the length of the 

 wire, a more uniform rate of propagation in the several parts of a continu- 

 ous extent is found than is the case when an adequate amount of electrical 

 influence is employed. 



When the notion was first brought prominently forward that the electrical 

 influence ought to pass along telegraphic wires with a velocity proportional 

 in reverse ratio to the square of the length of the wire, an hypothetical 

 plan was proposed for practically getting over this difficulty. This plan 

 was, to make the road for the electrical current of easier access, by rendering it 

 larger. It Avas conceived that if one wire was required to transmit signals 

 with equal facility and speed to another which was only one-sixth part as 

 long, the longer wire should be made of at least six times the capacity of 

 the shorter one. 



It was obviously a matter of primary importance to the cause of Atlantic 

 telegraphy that the deductions of this theory should be put to rigid experi- 

 mental proof, because, if they were correct, so large and ponderous a cable 

 would be required to carry even a single conductor, that the manufacture 

 and deposit in the Atlantic depths of such an unwieldy mass would be an 

 affair that mu>t prove of exceeding difficulty and cost, if not, indeed, alto- 

 gether impracticable. The Calais and Dover cable weighs eight tons per 

 mile ; the entire weight of a cable for Atlantic service, of only the same 

 dimensions as tins, would be t least 20,000 tons. As, therefore, the Atlan- 

 tic Cable would be required by theory considerably to exceed this, it is 

 plain that not even Scott Russell's Leviathan ship, which will he able to 

 move over the waves with an army of ten thousand men upon her decks, 

 could carry it to its destination. In the unsuccessful attempt to lay down 

 the Mediterranean cable, it was found to be a task of extreme difficulty, and 

 even danger, to manage the mechanical parts of the operation, owing to the 

 great weight of the cable held in suspension, and the vast strength and grip 

 of machinery required .to suspend. It may, therefore, be easily imagined 

 what the task would be with a cable weighing some ten tons per mile. The 

 weight in Atlantic depths, dependent upon itself, and hanging from the ship 

 and machinery would with it exceed twenty tons ; an amount equally incon- 

 venient and dangerous to the cohesion of the structure, and to the capabili- 

 ties of the apparatus used in paying out. 



The first experimental investigations upon this point comprised a series 

 of not less than two thousand observations. The experimenter worked 

 with a three hundred miles length.of wire, which he was enabled so to double 

 and treble at will, that it became for the time virtually a wire of twice or 

 three times the original capacity. The result was that it appeared the wire 

 of increased capacity did not transmit electrical signals with greater facility 

 and speed than the smaller one. With a length of 106 miles, the. velocity 



