Intelligence and Miscellaneous Articles. 4.75 



of preservation has, I conceive, advantages over those already used. 

 Common salt never presei-ves completely so as to enable the draw- 

 ings to withstand the action of the sun. Iodide of potassium seems 

 to require great delicacy in management, as when at all too strong- 

 it eats out the fainter tints, and is moreover subject to this incon- 

 venience — that sometimes the drawings so preserved, even when 

 kept in the dark, become entirely bleached and lose all traces of the 

 dark lines. This at least has happened to some drawings so pre- 

 pared by a friend of mine. There is no doubt that the hyposulphite 

 of soda is an excellent preservative, but it is a salt not easily pre- 

 pared and not likely to be in the hands of those who may wish to 

 make experiments on the subject. If you think these remarks 

 worth publishing, I shall be obliged by their insertion in your next 

 number. 



I am. Gentlemen, your obedient servant, 



J. C. CoNSTABtE. 



Jesus College, May 21, 1839. 



APPLICATION TO rHOTOGRAPHY OF THE LIGHT OF INCANDES- 

 CENT COKE. BY MR. R. MALLET. 



The following is an extract from the Proceedings of the Royal 

 Irish Academy (No. 16), for April 22nd, 1839: 



" Mr. Robert Mallet communicated a notice of the discovery of 

 the property of the light emitted by incandescent coke to blacken 

 photogenic paper ; and propose it as a substitute for solar light, or 

 that from the oxy-hydrogen blowpipe with lime. 



" One of the most important applications of the photogenic pro- 

 cess, as yet suggested, is its adaptation to the self-registering of 

 long continued instrumental observations. Unless, however, an ar- 

 tificial light of a simple and inexpensive character can be found to 

 supply the place of solar light at night, the utility of this applica- 

 tion will be much limited. 



" Few artificial lights emit enough of the chemical rays to act 

 with certainty on the prepared paper ; while those which are known 

 to act well, as the oxyhydrogen lime light, are expensive and difHcult 

 to manage. A considerable time since the author discovered that 

 the light emitted by incandescent coke at the 'Twyer' (or aperture 

 by which the blast is admitted) of a cupola or furnace for melting 

 cast iron, contained the chemical rays in abundance ; and on lately 

 trying the effect of this light on the prepared paper, he found it was 

 intensely blackened in about forty-five seconds. In the single ex- 

 periment made, the heat, which was considerable, was not separated 

 from the light; but the author purposed to make further experiments, 

 in which thi.s precaution will be attended to. 



" There is no difficulty to be ajjprcliended in contriving an appa- 

 ratus to l)urn a small quantity of coke at a high temi)erature. A 

 diagram of an apjiaratus for this purpose was shown. It consists of 

 a vertical tube, nine inches in diameter, lined witii refractory clay, 

 and closed at top and bottom. There is a grating about one foot 

 from the bottom, a little above which arc two opposite holes, into 



