192 THE SCIENTIFIC PAPERS OF 



on the way from Dover to Calais, it seemed to diminish much in 

 the same ratio as the light of the oil lamp diminished ; but there 

 would still remain the difference in favour of the more intense 

 light. If it possessed the same volume lit up the same area of 

 lenses its greater intensity would carry it to a greater distance ; 

 although he had ventured upon the supposition that the obstruc- 

 tion to that light would be greater on the part of matter suspended 

 in the air. Such might be the case ; and yet, as was now known, 

 that there was in the electric light a much greater volume than in 

 the ordinary oil or candle light, it still followed that the electric 

 light would, with its greater volume and greater intensity, penetrate 

 to a much greater distance. 



He desired to add a few explanations with reference to the 

 transmission of electric power to a distance, whether for the 

 production of light or for the production of force. The paper 

 stated that the weight of the conductor would increase as the 

 square of the distance ; but that proposition, although true in 

 itself, would, if it were accepted, lead to erroneous ideas with 

 regard to the power of transmitting force to a distance exceeding 

 perhaps \ mile. In order to get the best effect out of a dynamo- 

 electric machine there should be an external resistance not exceed- 

 ing the resistance of the wire in the machine. Hitherto it had 

 not been found economical to increase the resistance in the 

 machine to more than one ohm ; otherwise there was a loss of 

 current through the heating of the coil. If, therefore, there was 

 a machine with one ohm resistance, there ought to be a con- 

 ductor transmitting the power either to the light or the electro- 

 magnetic engine not exceeding one ohm. If, instead of going 

 1 mile, it was desired to go 2 miles, it would be necessary first of 

 all to employ a conductor twice the length, but that conductor 

 would give two ohms resistance, and would therefore destroy 

 much of the effect. To bring it back to one ohm resistance it 

 would be necessary to put down a second wire, or to double the 

 area of the first ; and in that case there would be a wire of twice 

 the length and twice the area, therefore four times the weight and 

 four times the cost. That pointed to an increase in the cost and 

 in the weight of the conductor in the square ratio of the distance. 

 But one circumstance had been lost sight of in the calculation 

 that having twice the area to deal with a second generator could 



