52 Mr. Edward Hophinson [Feb. 24, 



subject to loss of potential energy, whereas the energy of the steam 

 held back by valves of the engine suffers loss through radiation and 

 condensation. 



At Bessbrook the turbine and generator dynamo combined yield 

 60 per cent, of the energy of the water as electrical energy available 

 for work on the line, but when the load is reduced to a third of the 

 full load the efficiency is reduced to 33 per cent. So on the City and 

 South London line, a generator engine and dynamo will yield, when 

 working at their full load, 78 per cent, of the indicated horse-power 

 as useful electrical power, but at half load the efficiency falls to 

 65 per cent. Notwithstanding these conditions the generator station 

 of the City and South London line is producing electrical energy at 

 a cost of l*56d. per Board of Trade unit, which is less than the 

 annual average cost of production of any electric station in England, 

 with the single exception of Bradford, which has the advantage both 

 of cheap coal and cheap labour. In output it is the largest of any 

 Electric Generating Station in England, the total electrical energy 

 delivered in 1892 being 1,250,000 Board of Trade units, the 

 second on the list being the St. James and Pall Mall with 1,186,826 

 units. 



Let us pass now to the consideration of the distribution of the 

 electric power along the line. I have equipped the three model 

 tracks before you with three different kinds of conductors. In two 

 of them the rails of the permanent way, which are necessarily 

 uninsulated, are made use of for the return current. This plan, with 

 I believe the almost single exception of the Buda-Pesth Tramway, 

 has been universally adopted with the object of saving the cost of a 

 return conductor ; but it is doubtful whether such an arrangement 

 can be considered final, for it must necessarily create differences of 

 potential in the earth, which already in some instances have had 

 disturbing effects upon our observatories, or upon our telegraph and 

 telephone systems. It appears to be probable in the more or less 

 distant future that the use of the earth for the passage of large 

 current will be prohibited by legislation ; and that it will be reserved 

 for the more delicate and widely extended operations of telegraphy 

 and telephony. These disturbances may of course be easily avoided 

 by the use of an insulated conductor for the return circuit; and it 

 may be that our legislature, looking forward to a remoter future, 

 when electrical forces may be utilised, compared with which even 

 those involved in our present telegraj)hs and telephones are incon- 

 siderable, will insist upon all, — tramways, telegraphs and telephones, 

 — using an insulated return ; a course which I venture to think would 

 be of present benefit to these services, as well as a safeguard for the 

 interests of the future. In the case of conductors which are in such 

 a position that contact may be made from them to the ground through 

 the body of a horse or some other animal coming into contact with 

 them, there is another strong argument for an insulated return, as 

 many animals, and notably horses, are far more sensitive to electric 



