330 Applicability of the Electric Light to Lighthouses. 



collected together by means of a commutator, the alternate 

 positive and negative currents being brought into one direction. 

 The combined current is conveyed, by a thick wire, from the 

 engine-house to the illuminating apparatus, where it forms a 

 continuous and brilliant spark between two charcoal points, 

 which are maintained at a proper distance apart by means of a; 

 balance arrangement, and an electro-magnet, round which the 

 wire coils. The charcoal points are consumed in about three 

 hours and a half; after which period they are changed, 

 without extinguishing the light, as it is the kindling of the 

 second pair which puts out the first. In more recently con- 

 structed machines, a smaller number of magnets and soft iron 

 cores are employed. 



At the close of 1859, experiments were commenced by 

 the French Lighthouse Engineers, with an electro-magnetic 

 machine obtained from the Alliance Company. This apparatus 

 consisted of fifty-six magnets, distributed in seven equidistant 

 planes, on the angles of a right octagonal prism. The electro- 

 magnetic armatures, which were fixed on discs turning round 

 the axis of the prism, and were made to revolve by a steam-en- 

 gine of two-horse power, passed between the groups of magnets. 

 The alternate currents were brought into the same direction, 

 and united into one, without a commutator. Sixteen changes 

 of direction corresponded to every revolution of the disc ; and 

 a maximum of intensity was obtained, when the machine made 

 about four hundred revolutions in a minute ; in which case, the 

 current was reversed six thousand four hundred times in a 

 minute. 



The electric lamp, which was used with these experiments, 

 is so contrived as that the charcoal points approach each other, 

 according as they are consumed, without, in any case, coming 

 into contact. When they are at the proper distance apart, two 

 forces, one derived from a spring, the other from an electro- 

 magnet, the coil of which is traversed by the current, balance 

 each other, and the points remain at rest ; but when, on account 

 of increased distance between these points, the power of the 

 current is diminished, the spring comes into action, and causes 

 the points to approach, until their motion is stopped by the 

 restoration of energy to the electro-magnet. This apparatus may 

 be adjusted to the power of any given current ; and, "notwith- 

 standing its delicacy, it has been found to work with great 

 precision. Much, however, depends on the nature of the 

 charcoal points ; those made from the deposit on the interior 

 of gas retorts, and obtained in commerce, do not give complete 

 satisfaction, and it is not easy to obtain others of a better kind, 

 and quite free from objection. The want of homogeneity in 

 the charcoal causes constant variations in the light, however 



