108 Dr Brewster on a nciv Monochromatic Lamp. 



Art. XV. — Account of a New Monochromatic Lamp depend- 

 ing on the combustion of' compressed Gas. * By David 

 Brewster, LL. D. F. R. S. L. and E. 



On the 21st of February 1826, I exhibited to the Society of 

 Arts, the experiment of converting the exploding flame of a 

 portable gas lamp into a mass of homogeneous yellow light by 

 crossing it with a platinum wire or a film of mica ; and it 

 occurred to me, that a permanent monochromatic flame might 

 be produced by causing a spiral of platinum wire to revolve 

 in the lower part of the flame by means of its impulsive force. 

 As the spiral wire, however, required to have its surface sup- 

 plied with a thin coating of a soapy or greasy fluid, and was 

 oesides liable to go out of order, I constructed a broad collar 

 with coarse cotton wick, which could be placed either upon or 

 above the ringy^of the subsidiary burner, shown in Plate IT. 

 Fig. 3, and already described. This collar was soaked in a 

 saturated solution of common salt. 



When the gas is allowed to escape at M, with such force 

 as to produce a long and broad column of an explosive mix- 

 ture of gas and atmospheric air, the bluish flame produced by 

 the explosion is made to pass through the saturated collar, 

 and is converted by it into a mass of homogeneous yellow light. 

 The collar will last a long time without any fresh supply of 

 salt, so that the gas lamp will yield a permanent monochro- 

 matic flame, during the longest series of optical experiments. 

 The eff'ect of this instrument is quite surprising. The inten- 

 sity of the yellow light is very great, and may be readily in- 

 creased for microscopical purposes by condensing it with mir- 

 rors or lenses. 



In place of a collar of cotton wick, a hollow cylinder of 

 sponge with numerous projecting tufts may be substituted ; 

 or a collar may be similarly constructed with Asbestos cloth ; 

 and, if thought necessary, it might be supplied with a saline 

 solution from a capillary fountain. 



♦ Exhibited to the Society of Arts, May 1st, 182C. 



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