114 Mr. Talbot on the Nature of Light, 



tion of the metal calcium, an idea which in the first place 

 seems contradictory in itself, and at any rate is destitute of 

 proof. The great heat gradually dissipates the lime, and 

 this circumstance is liable to be mistaken for a necessary 

 consequence of the experiment instead of being an accidental 

 accompaniment of it, which ought to be avoided if we wish 

 to obtain an insight into the cause of the phenomenon. 

 In order to do so, we must try the experiment at a lower tem- 

 perature, at which lime is perfectly fixed. The first experi- 

 ments of this kind that I know of were published by Mr. Ca- 

 meron of Glasgow, and Sir David Brewster in 1820 {vide 

 Edinb. Phil. Journ., vol. iii. p. 343). 



The best method of proceeding is the following : 



Dip a piece of white paper in a solution of muriate of lime, 

 and then wipe off the superfluous liquid, leaving the paper a 

 little moist. Cut a strip of it, and hold the extremity in the 

 flame of a spirit-lamp. After a minute or two the carbona- 

 ceous matter of the paper will be dissipated, and the lime will 

 alone remain, in the form of a perfectly white minutely divided 

 network. This will soon become very vividly ignited and 

 emit a bluish-white light. Practice is requisite in this expe- 

 riment to obtain the most successful result. When the in- 

 candescence has become brilliant, it remains so for any length 

 of time unaltered and without diminution as long as the lamp 

 is supplied with alcohol. 



Now, the chief thing that merits observation is, that the 

 original weight of the lime is only a small fraction of a grain, 

 and that no diminution of it is perceived at the end of the ex- 

 periment. It is surely unnecessary to advance any further 

 argument to prove that the light is not really emitted by the 

 lime in the manner in which a candle emits light, by the com- 

 bustion of its particles, but that it acts in some wholly different 

 manner. In short, we see that the mere presence of the lime, 

 in a heated state, is the cause of the light. 



In order to know to what degree the luminosity of a flame 

 might be increased by the presence of lime, I made the fol- 

 lowing experiment: — A flame of alcohol was gradually dimi- 

 nished as much as possible, by reducing the wick to a single 

 thread, and by other contrivances. 



In this state, when the minimum of combustion was attained, 

 the flame was reduced nearly to the size of a pea, and it gave 

 a very faint blue light. When placed in a dark room, the 

 flame itself was visible, but nothing could be seen by its light, 

 not even any part of the lamp itself. A particle of lime (re- 

 served from a former experiment) was then placed in the flame. 

 The lime immediately became incandescent, and light enough 

 was emitted by it to tell the hour on a watch at the distance 



