. Machinery and processes of the industrial arts, and apparatus of the exact sciences. eve, as concentrated by the catadioptricsystem of Fresnel, was found to be equivalent to that of three thousand INTENSITY OF THE ELECTRIC LIGHT. 423 five hundred Carcel burners. The light which it replaced, and that ofthe companion light which for a time remained, had only the force ofsix hundred and thirty Oarcel burners. After the new light had beenput into operation, the point of principal interest first attended to wasto ascertain, by comparative observations, the mean relative visibility orrange of visi
. Machinery and processes of the industrial arts, and apparatus of the exact sciences. eve, as concentrated by the catadioptricsystem of Fresnel, was found to be equivalent to that of three thousand INTENSITY OF THE ELECTRIC LIGHT. 423 five hundred Carcel burners. The light which it replaced, and that ofthe companion light which for a time remained, had only the force ofsix hundred and thirty Oarcel burners. After the new light had beenput into operation, the point of principal interest first attended to wasto ascertain, by comparative observations, the mean relative visibility orrange of visibility of the two lights. Observations were accordinglymade three times every night by the keepers of the three lights atHonrleur, distant fifteen kilometres, or eight and one-tenth miles; atFatouville, distant twenty-one and a half kilometres, or eleven and six-tenths miles; and at Ver, distant forty-six and five-tenths kilometres, ortwenty-five and one-tenth miles. The following table presents the results: Place of observation. Distance. S o a> a d M 15 Honfieur .FatouvilleVer This table does not furnish a very fair test of the relative value of thelights. During the greater number of the nights of observation whenboth lights were seen, a much feebler light than either would probablyhave been equally visible, especially from the nearer points. Duringmany of those in which neither was seen, it is probable that a muchmore powerful one than either would have been unobserved also. Thetable shows, nevertheless5 that while the electric light is superior to theother, it is not so much superior as might have been anticipated. Itshows, further, that its superiority is apparently more marked as thedistance is greater; a fact, however, which is associated with the importantadditional fact that both lights are less frequently seen at great distances,or, in other words, are seen at such distances more frequently in clearweather, when the rays of hi
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