244 THE SCIENTIFIC PAPERS OF 



more contact pulleys, and to be again deposited behind the train. 

 The central rail or copper conductor may, however, be entirely 

 dispensed with if the two rails laid upon wooden sleepers are con- 

 nected the one with the positive and the other with the negative 

 pole of the dynamo machine. In this case care must be taken to 

 insulate the wheels on one side of the train from those on the other , 

 an object that can be attained by the adoption of wheels with 

 wooden centres, and the metallic tires of the wheels on the one 

 side must be put into metallic connection with the one pole, and 

 the other with the other pole of the machine or machines on the 

 train. Practice alone can determine which of these modes of 

 construction is the best, but each can be made efficacious, and the 

 preference will be due to economical or structural considerations. 



The length of this paper has already exceeded, I fear, reason- 

 able limits, or I might be tempted to enlarge upon the subject of 

 the electric transmission of power. Enough has been said, how- 

 ever, to illustrate some of the uses to which this new form of 

 energy may be rendered available for the purposes of man. 



(At the close of the paper a dynamo machine was set to work, 

 and supplied motive power to a circular saw, which cut up several 

 pieces of timber from two to three inches square.) 



In the discussion of the Paper 



"ON LIGHTHOUSE CHARACTERISTICS," 



By SIR WILLIAM THOMSON, 



DR. C. W. SIEMENS, F.R.S.,* said the subject was one of great 

 interest to him, but he had not given sufficient attention to the 

 details to be able to speak with uny authority upon it. He might 

 say a word or two, however, on the probability of seeing the elec- 

 tric light established for the purpose of giving those flashes which 

 had been referred to. He might certainly say that the electric 



* Excerpt Journal of the Society of Arts, Vol. XXIX. 1880-81, p. 313. 



