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On the Illumination of Light-houses. By Lieut. Thomas Drummond, 

 of the Royal Engineers. Communicated by Lieut. -Colonel Colby, 

 of the Royal Engineers, F.R.S. Read June 17, 1830. [Phil. 

 Trans. 1830, p. 383.] 



The author, after briefly describing the different methods at pre- 

 sent employed for illuminating light-houses, proceeds to detail what 

 he considers an improvement upon those now in use. This consists 

 in substituting for the Argand burner a small ball of lime, ignited by 

 the combustion of oxygen and hydrogen. 



From this small ball, only three eighths of an inch in diameter, so 

 brilliant a light is emitted, that it equals in quantity about 13 Argand 

 lamps, or 120 wax candles; while in intensity, or intrinsic bright- 

 ness, it cannot be less than 260 times that of an Argand lamp. These 

 remarkable results are deduced from a series of experiments made 

 lately at the Trinity House ; and having been repeated with every 

 precaution, and by different individuals, there seems no reason to 

 doubt their accuracy. 



In the best of our revolving lights, such as that of Beachy Head, 

 there are no less than 30 reflectors, 10 on each side. If, then, a sin- 

 gle reflector, illuminated by a lime ball, be substituted for each of 

 these 10, the effect of the three would be 26 times greater than that 

 of the 30. On account of the smaller divergence of the former, it 

 would be necessary to double their number, placing them in a hexa- 

 gon instead of a triangle ; in this case, the expense is estimated at 

 nearly the same. This method was tried lately at Purfleet, in a tem- 

 porary light-house, erected for the purpose of experiments by the 

 Corporation of the Trinity House ; and its superiority over all the 

 other lights with which it was contrasted, was fully ascertained and 

 acknowledged. 



On the evening of the 25th of May, when there was no moon- 

 light, and the night dark, with occasional showers, the appearance 

 of the light, viewed from Blackwall, a distance of ten miles, was de- 

 scribed as being very splendid. Distinct shadows were discernible, 

 even on a dark brick wall, though no trace of such shadows could 

 be perceived when the other lights, consisting of 7 reflectors, with 

 Argand lamps and the French lens, were directed on the same spot. 



Another striking and beautiful effect, peculiar to this light, was 

 discernible when the reflector was turned, so as to be itself invisible 

 to the spectator. A long stream of rays was seen issuing from the 

 spot where the light was known to be placed, and illuminating the 

 horizon to a great distance. As the reflector revolved, this immense 

 luminous cone swept the horizon, and indicated the approach of the 

 light long before it could itself be seen from the position of the re- 

 flector. These singular effects must not, however, be understood as 

 constant accompaniments of this light ; for on a moonlight night, or 

 when the weather is very hazy, they cease to appear. 



