208 THE SCIENTIFIC PAPERS OF 



Dr. Siemens apprehended that few persons would coincide with 

 Mr. Wigham in that view. It might be an advantage in looking 

 at a light at a short distance, but the ex-focal light would give 

 very little effect at a great distance. In regard to a powerful 

 light, therefore, and a large dioptric apparatus, the question was, 

 how much light could be produced within a reasonable focal 

 sphere ? and in that respect the electric light had a great ad- 

 vantage. In the case of the Lizard light, as much as 16,000 

 candle-power was developed, virtually, in a point ; and if that 

 amount of light was distributed over a reasonable surface, he was 

 sure that greater penetrating power would be obtained than could 

 be produced in any other way. Then the question arose, was not 

 the electric light too expensive ? In that respect the paper 

 furnished valuable information. It showed that the electric light 

 was relatively expensive when it was produced in small quantities, 

 but that it became cheaper when produced in a large volume. 

 Thus, the electric light at the Lizard, though twenty-three times 

 more powerful than the oil lamp, was only double the cost ; and, 

 inasmuch as it had on foggy nights penetrating power to double 

 the distance, he thought a satisfactory result had been actually 

 obtained, considering that the effect of light diminished as the 

 square of the distances, and that it was necessary to allow a large 

 margin of loss in the haze. In fact, the electric light, when 

 regarded a priori, was necessarily a very cheap light, because, as 

 Dr. Hopkinson had said, a well-constructed dynamo-electric light 

 apparatus produced in the shape of current 90 per cent, of all the 

 energy expended in moving the machine. That was a result 

 which, he believed, was unique in the transformation of energy. 

 He never ventured to claim more than 70 per cent., but he saw 

 no reason to doubt Dr. Hopkinson's investigation. With such a 

 power it was only a question of judicious application in order to 

 realise the advantages which it promised. He was sorry to learn 

 that any trouble had occurred with the Lizard light. He had not 

 heard of it, and was under the impression that the light had 

 answered exceedingly well. It might be said, however, that in 

 riding a racehorse more care had to be exercised than in riding a 

 carthorse ; and that for the same reason the use of a light equal 

 to 16,000 candles required more care than an oil lamp of 700 

 candles. He had no doubt that, under the able management 



