hy means of ordinary Artificial Light 173 



subject has, upon my suggestion, been inserted by the Royal 

 Scottish Society of Arts among those recommended by them 

 for consideration. 



This could, perhaps, be done to most advantage by a pure 

 white flame, if such a flame can be produced by convenient 

 and unexpensive means, and without deleterious efi^ects on the 

 air, other than those necessarily produced by combustion.* 

 Or, failing that, it might be done, although not so conve- 

 niently or satisfactorily, by blue flame, if producible on the 

 conditions just mentioned, used along with ordinary orange 

 flame, in such ratio as to neutralize it, on the principle to be 

 immediately noticed. In the mean time, I submit to the So- 

 ciety a few observations on the application of a simple and 

 obvious method of eff'ecting the same object, by using any of 

 the ordinary artificial lights, and absorbing the excess of 

 orange by interposing a transparent medium of a proper colour. 

 I had felt very strongly the bad eff'ect of ordinary artificial 

 light on pictures, in using portable dioramas, which I lately 

 submitted to this Society, which led me to endeavour to de- 

 vise a remedy ; and I have found it to be completely obviated 

 by the application of that method, in the manner which I shall 

 now explain. 



Artificial light is most conveniently obtained by using car- 

 buretted hydrogen gas, such as that made in a proper manner 

 from parrot or cannel coal ; and a powerful light is easily 

 obtained in this manner. Gas from common coal is much in- 

 ferior. Oil is not so convenient or so cleanly as gas. Candles 

 are inconvenient from their varying in height, which, for 

 many purposes, renders frequent adjustment necessary; and 

 when they are enclosed in the manner which is generally ne- 

 cessary, even the least fusible are liable to melt, although 

 they have as large a supply of cool air as can conveniently 

 be given, unless there be very few of them, which makes the 



* The " Bude Light," which is produced by a stream of oxygen within a 

 flame of carburetted hydrogen, such as coal gas, and which is very brilliant, has 

 still so much of the orange tinge as to render it unfit to be used unmodified, as 

 being white light ; and, even if it were white, it is much more troublesome and 

 expensive than the method of obtaining white light to be now proposed. 



