180 Mr. J. G. Children on a New Light for Optical Purposes. 



in the proportion, by measure, of one partofcamphine to eight 

 parts of spirit of wine, of the specific gravity of •84'1 at 60° F. 

 (equivalent to the spirit of commerce of 60'^}, we obtained a 

 light amply sufficient, not only for my friend's dissolving views, 

 but also for his microscope and physioscope, and perfectly 

 free from all danger, or even possibility of explosion. My 

 friend's screen is about 22 x 18 feet ; and if it were twice as 

 large, the light is quite capable of illuminating it brilliantly ; 

 and it shows a microscopic object, magnified from half an inch 

 to thirty feet, or 720 times, linear, with great distinctness and 

 beauty. I do not mean that our toy can be compared to the 

 almost solar intensity of the oxy-hydrogen light, also invented 

 by the late Lieut. Drummond*, and now in common (too 

 common ?) use ; but in a trial I made the other day in Francis 

 Street, with an apparatus hastily put together for the purpose 

 by Mr. Collins, I found its effect, measured by one of Wheat- 

 stone's photometers, equal to that of seventy-six of Brecknell 

 and Turner's best platted-wick wax candles ; and in several 

 trials with our own apparatus, more carefully arranged, and 

 with thoroughly well and recently burnt lime (an essential 

 caution), we have found it quite equal to 108 of the same can- 

 dles, and on one occasion to 120 ! The oxy-hydrogen light at 

 Mr.Collins's, which was splendidly brilliant, being compared in 

 the same manner, was found equal to 121 of the same candles. 



In these experiments, no portion of the rays from either of 

 the lights was intercepted ; our object being to ascertain the 

 comparative illuminating power of their entire surfaces, and 

 not their comparative intensities onlyf. 



Were it not for the peculiar odour of the so-called naphtha 

 or coal-oil, which to some persons is highly offensive, even in 

 its purest state, it might, when highly rectified, be advan- 

 tageously substituted, in an oeconomical point of view, for the 

 spirit of wine. Four ounces of camphor dissolved in a pint of 

 that liquid, gives, under the same circumstances, nearly as 

 brilliant a light as the spirit and camphine. 



The light from camphine alone is for a few seconds intensely 

 brilliant, but it is soon quenched in the enormous mass of un- 

 burnt carbon, which partly condenses on the lime and partly 

 escapes into the atmosphere, filling the whole apartment with 

 a dense and almost suffocating cloud of floating black particles. 



* Philosophical Transactions, 1830. 



+ Some attempts indeed were made in Francis Street to compare the 

 intensities alone ; but the apparatus, from want of time to prepare a better, 

 was too imperfect to allow me to place any confidence in the results. As 

 far as they went, they were greatly in favour of the superior intensiti/ of the 

 oxy-hydrogen light. I hope to repeat the trials with a more refined appa- 

 ratus. 



