184 G. Tait, Esq., on producmg White or Neutral Lights 



the solar lamp may be used, which will produce white light 

 at the same expense as orange light from tallow candles, and 

 at less than half the expense of wax candles, independently 

 of the diminution of the ratio of orange, in consequence of the 

 great brightness of the flame of that lamp. 



The want of intensity of the light, as thus modified by the 

 blue medium, is, to a certain extent, a defect for some parti- 

 cular purposes. But, for general use, the intensity of arti- 

 ficial light is often subdued and diffused by ground glass or 

 other means used expressly for that purpose. And any quan- 

 tity of neutral light may, of course, be obtained by using a 

 proportionably greater quantity of flame ; and, if necessary, it 

 may be concentrated by using lenses, or metallic reflectors 

 properly constructed and applied ; the use of which, indeed, 

 where applicable, may render a great increase of flame un- 

 necessary. And I am not aware of any other means so conve- 

 nient and unexpensive of producing the uniform neutral light, 

 or artificial daylight, so desirable for many purposes. 



I submit these imperfect hints with diffidence. But, per- 

 haps, they may be of this use, at least, that they may tend 

 to draw the attention of more competent persons to the pro- 

 duction of white or neutral light. 



Edinburgh, 1846. 



Postscript. — Since writing these observations, my attention 

 has been directed to a short popular treatise " On the Influ- 

 ence of Artificial Light, in causing impaired Vision, and on 

 some Methods of Preventing or Lessening its Injurious Eff^ects 

 on the Eye," by the late Dr James Hunter of Edinburgh, pub- 

 lished in 1840, of which I was not aware, and which appears 

 to be a judicious and intelligent work. One of the methods 

 recommended by him, is founded upon the sound and obvious 

 principle of correcting the excess of orange in aHificial light, 

 in order to produce white light, or something near it. But, 

 although the means proposed by him for eff*ecting this may 

 be sufficient as palliatives for medical purposes, they appear 

 not to be suitable for the purposes of art. One of those 

 means is to use, over an argand flame, or a flat flame, a co- 

 nical reflector, the inside of which is without gloss, and is 



