336 Dr. C. William Siemetis [March 12, 



form of the machine was not materially altered by this change, 

 which consisted in so arranging the wire on the rotating helix and on 

 the exciting electro-magnets, that the maximum current produced for 

 the power expended was attained when the outer resistance was such 

 as was usually required. 



Amongst the applications of the dynamo-electric current, the 

 lecturer showed in the first place that of the transmission of power, 

 illustrating this portion of his subject by working a circular saw, 

 receiving its motion from a dynamo-electric machine (constructed 

 according to the modified plan alluded to) placed in the basement 

 of the Eoyal Institution and receiving motive power in its turn from 

 a gas engine. It was shown that by such an arrangement 60 per 

 cent, of thfe engine power expended could be utilized at another 

 place, and that thus natural sources of power, such as waterfalls, 

 might be made available for supplying motive power at distances even 

 of twenty or thirty miles ; or power might be transmitted to the 

 depths of mines and collieries by the establishment of a stout leading- 

 wire connected with an electro-motor on the bank. 



The lecturer next described a novel application of the dynamo- 

 electric current for the propulsion of tramway cars upon railways, by 

 preference upon elevated railways. Dr. Werner Siemens had made 

 such an application very successfully last year in connection with a 

 Berlin Exhibition, and the experiment would very shortly be repeated 

 at the Crystal Palace. One of the carriages composing the train was 

 fitted with an ordinary dynamo machine, and another similar machine 

 was worked on terra firma by engine power. A central rail or con- 

 ducting rope was introduced for the conveyance of the current, the 

 return circuit being completed through the side rails, and the person 

 in charge on the train could by moving a handle start and stop the 

 train as required. The tractive force was considerable, and increased 

 with the resistance, amounting in ascending an incline to 200 kilo- 

 grammes, and falling to 70 or 80 kilogrammes on level ground. 

 From thirty to forty persons were conveyed easily at a speed of from 

 ten to twelve miles an hour. 



Dr. Siemens explained that whenever a current was passed through a 

 conductor, a loss was incurred varying as the square of the intensity of 

 the current and as the resistance encountered, but that what was loss 

 of current when the object was the simple transfer of electrical energy 

 might be turned into a gain where light and heat were to be produced. 

 Platinum and iridium were notoriously bad conductors, and on putting 

 a piece of wire of these metals into a circuit they become hot and 

 luminous, as was well known. It would readily be conceived that 

 the greater the electrical resistance in any one point of a circuit the 

 greater must be the luminosity produced, and Sir Humphry Davy 

 had shown as far back as 1810, before the Koyal Institution, that 

 the greatest local resistance, and the highest degree of heat and 

 luminosity, could be produced in the electric arc between two carbon 

 electrodes placed a short distance apart. 



