LIGHTHOUSES, RECENT PROGRESS IN. 



The total number of lighthouses and beacon 

 lights maintained by the Lighthouse Establish- 

 ment in the United States in 1898 was 1,179; but 

 as this figure includes many insignificant lights 

 on the seacoast and harbors, it may be safely as- 

 sumed that only about 500 are lighthouses proper, 

 and only a comparatively small number of these 

 maintain lights of the first order. The increase in 

 number in the past decade has been about 45 per 



A MODERN 8TEEL TOWER, AT STURGEON BAT CANAL. WIS., 

 WITH A I.ASTHKN OF THE THIRD ORDER. 



cent. In the United Kingdom the Admiralty list 

 slmws a total of about 1,100 lights, a gain of 200 in 

 ten years. Kleven to 12 per cent, of these are sea 



which are shifted as required by changes I;: the 

 channels. 



In the I'nited States mineral oil is preferred as 

 ii'i illiiminant and is used almost altogether, though 

 there are a few electric lights. In the United 

 Kingdom either gas or petroleum are used for 

 Illuminating, according to convenience and local 

 conditions, and in a few cases electric lights are 

 used. While the arc light may be made to develop 

 exceptional brilliance, it is not as acceptable for 

 lighthouses as for illumination on land, because it 

 is so much affected ly atmospheric conditions. 

 During foggy weather, when the strength and pene- 

 trating power of a light are most needed, the 

 electric light is most liable to dim : hence its value 

 on the water is much reduced, and although, when 

 first introduced into lighthouse use, it was com- 



mended, it is now generally regarded with small 

 favor. In United States usage, six orders of lights 

 are maintained : the first of 5 wicks, having 450 

 candle power ; the second of 3 wicks, having 163 

 candle power ; the third of 2 wicks, having 78 candle 

 power; the fourth of 1 wick, having 32 candle 

 power; the fifth of 1 wick, having 18 candle 

 power; and the sixth of 1 flat wick, having 12.5 

 candle power. The light given out and the 

 distance from which it can be seen vary so much 

 under different conditions and with different 

 observers that the candle-power statement hardly 

 conveys a correct idea of the power of the lights. 

 There is also a considerable difference in methods 

 of estimating candle power. The experiments of 

 the Lighthouse Board indicate that a white light of 



1 candle power is visible at a distance of 1 mile, 



2 candle power at 2 miles. 3 candle power at 3 

 miles, while at 4 and 5 miles the power has to be 

 increased to 23 and 33 candle power respectively 

 to be seen clearly. Of course, the conditions of the 

 atmosphere as to dryness or humidity, dustiness or 

 freedom from dust, are so varied that these figures 

 can be taken only as approximate, giving a fair 

 average in moderately clear weather. With colored 

 lights the candle power requires to be increased 

 enormously, as the colored glass absorbs a very 

 large percentage of the light. 



There has been a gradual tendency to increase 

 the size of lanterns for sea lights, and 14 feet di- 

 ameter has succeeded 12 in several instances. Cir- 

 cular galleries are provided both inside and outside 

 for access and cleaning. The best plate glass, half 

 an inch thick, is used, and there have been improve- 

 ments in the ventilators. The use of mixed lights 

 that is, lights of both fixed and rotating sections 

 has materially decreased, and they are now re- 

 garded with disfavor. Colored lights also have 

 been generally abandoned for sea lights, though 

 still maintained in harbors. It was formerly 

 thought to be an advantage to differentiate the 

 colors of lights along a coast, in order that mari- 

 ners might not mistake one light for some neigh- 

 boring light ; but this advantage has been more 

 than offset by the loss in distance from which a 

 colored light can be distinguished, and it is found 

 possible to differentiate the lights of a coast equally 

 well by giving a different time to the flashes. The 

 flashing light not only proves the best safeguard 

 against mistakes, but it increases materially the 

 distance from which a light is perceptible. The 

 general adoption of flash lights for sea use has been 

 followed by a shortening of the period of the 

 flashing. Whereas intervals of one minute were 

 formerly employed between flashes, the periods are 

 now commonly reduced to twenty, ten, or five sec- 

 onds, and the tendency is toward an even greater 

 reduction, as it has been demonstrated that the 

 best results are obtained with the shortest appre- 

 ciable intervals. Lord Kelvin has gone so far as to 

 advocate the use of flashes separated only by frac- 

 tions of a second. 



The flashing of the light is obtained in the case 

 of electric or other lights by regular occultation, as 

 by a rotating annular lens bearing dark shades. 

 and in the case of oil lights it is often obtained Ir- 

 regular raising and lowering of the wicks. In 

 order that a light may be visible to the greatest 

 distance, it is not only necessary to secure a short 

 interval of flash, but it must also have the greatest 

 intensity of beam. In other words, the greatest 

 portion of the light must be turned in the desired 

 direction, and this increased power has been sought 

 by the substitution of annular for cylindrical 

 lenses, and by rotating for fixed sections. Lenses 

 have been given a longer focal distance and larger 

 condensing surfaces. Variations and extensions of 



