680 THE APPLICATIONS OF PHYSICAL FOUCES. [BOOK v. 



those on which it is of the greatest importance to sailors to be 

 sure of their position. The increase of the number of Carcel lamps 

 does not solve the difficulty, for the range depends not only on the 

 apparent diameter of the light, but on its intrinsic illuminating power. 

 The employment of the electric light, the intensity of which is so 

 considerable, naturally suggested itself; but its application was not 

 possible until a suitable regulating apparatus and machines capable 

 of producing a sufficient amount of light had been discovered. 

 Regulators such as Serrin's or Foucault's satisfied the first of these 

 conditions ; Magneto-electric machines have enabled us to satisfy the 

 second. 



The Alliance magneto-electric engines of the lighthouse of La Heve, 

 on the Straits of Dover, are set in motion by two steam-engines of 

 five-horse power between them ; with a velocity of rotation of four 

 hundred turns a minute the maximum intensity is obtained. The 

 light (reduced to the horizon) produced by a machine with four discs, 

 equals that of 3,500 Carcel lamps ; with a machine of six discs, the 

 effect of 5,000 lamps is obtained, with a range of twenty-seven 

 nautical miles, or fifty kilometres. This powerful source of light 

 results from the association of the induced currents which arise from 

 the instantaneous action of forty-eight magnets on the ninety-six 

 moving bobbins in each magneto-electric machine. 



Four of these Alliance machines are at work in the lighthouse of La 

 Heve. All the apparatus is in duplicate, in order that the immediate 

 substitution of one lamp for another may not produce any discontinuity 

 of the light. The lamps are set upon little pairs of rails, ending in 

 the centre of the lenticular apparatus, fixed one alongside the other in 

 the same lantern. The regulators employed are Serrin's. This new 

 method of illuminating lighthouses has been recently adopted along 

 the Suez Canal. 



Not only does the electric light produced by electro-magnetic 

 machines surpass in intensity that afforded by oil-light apparatus in 

 the ratio of five to one at least, giving a light equal to 400,000 candles, 

 but it is also more economical. 1 While a lighthouse provided with 

 ordinary first-class lamps costs three francs seventy cents an hour, an 



1 M. Van Malderen is about to construct a new pattern of engines with four 

 discs, M'hich will be more powerful, with equal velocity, than the old ones with six 

 discs. They give the light of 230 Carcel lamps instead of 180. 



