110 ANNUAL OF SCIENTIFIC DISCOVERY. 



apparatus two, only one lamp being used at a time. Mr. Holmes in- 

 cludes in his plan the use of all these lamps and apparatus, because 

 of the facility of rapid change in the lamps and carbons, and they 

 cause no alteration in the magneto-electric machines, wires, or en- 

 gines, which are the same as were employed at the South Foreland. 



Beside the electric apparatus, the light from which passes through 

 the upper panes of the lantern, the original reflectors and their lamps 

 are retained in place, so that they can be at once substituted for the 

 electric light if any accident or failure should occur to the latter, 

 and also may be used in conjunction with the electric light in a com- 

 parison of one with the other. 



In one of his reports on the Dungeness light, written during the 

 past year, Prof. Faraday mentions an interesting experiment. Ar- 

 rangements were made on shore (Mr. Holmes being in charge of the 

 light), by which observations could be taken at sea about five miles 

 off, on the relative light of the electric lamp and the metallic reflect- 

 ors with their Argand oil lamps. At the given distance the eye 

 could not separate the two lights, but by the telescope they were dis- 

 tinguishable. The combined eifect was a glorious light up to the five 

 miles ; then, if the electric light was extinguished, there was a great 

 falling off in the effect ; though, after a few moments' rest to the eye, 

 it was seen that the oil lamps and reflectors were in their proper 

 state. On the other hand, when the electric light was restored, the 

 illumination became again perfect. 



Then, whilst both were in action, the reflectors were shaded, and 

 the electric light left alone ; but the naked eve could see no sensible 



o / 



diminution ; nor when the reflectors were returned into effectual use 

 could it see any sensible addition to the whole light power, though 

 the telescope showed that the alteration in the lantern had taken 

 place at the right time. Such was the power of the electric light, 

 that the addition or subtraction of the light of a fully effective set of 

 reflectors, with their lamps, would not have been sensible to a mariner, 

 however observant he might have been. 



Prof. Faraday enumerates some points which are against, and oth- 

 ers in favor of, the light. In the first place, the simplicity of the 

 present system is very great, compared with that of the electric 

 light : only two keepers are required to a lighthouse ; they need pos- 

 sess no special knowledge ; ordinary attention is all that is necessary ; 

 and thus failures of the light are almost impossible. In the new sys- 

 tem a second set of men will be required to attend the engines, and 

 there must be among them one or more who understand the principle 

 and construction of the lamp in the lantern, of the magneto-electric 

 machines, the steam-engines and the condensers, and be able to make 

 effectively the repairs necessary to the apparatus. In the next place, 

 the expense of the new system must be large compared with that of 

 the present system. Other objections have been made, of which 

 Prof. Faraday cannot see the force ; namely, that the light is too 

 bright, - - that it gives a false impression of the distance of the light- 

 house, and that it blinds the eyes of the mariners to the percep- 

 tion of the lights on board vessels between it and them. These ob- 

 jections, he says, if they have any force, must be judged by mariners 

 themselves. 



