138 Brief Notice of a Discovert/ on the Safety-lamp. 



Much remains to be ascertained in relation to different lati- 

 tudes, and the effects produced in different parts of tlie dav. 1 

 am unwilling to attempt to crowd your pages with too manv of 

 my own remarks, and hope that some of your correspondents 

 will favour us with their observations. • 



Yours respectfully. 

 Gray Friars Priorv, Norwich, T. DrUMMOND. 



Jan. 0. 1817. 



XXXII. Brief Notice nf a Discovery by which Sir H. Davy's 

 Safe-larfip may be made to re-light itself when extinguished 

 in the Mine. By J. Murray, Estj. 



To Mr. Tilloch. 



Sir, — XT gives me much jjleasure to announce to vou the 

 following important fact : — a method by which Sir Humphry 

 Davy's safe-lamp may be made to relight itself when ex- 

 tinguished by an inflammable medium. The experiment was 

 repeated eight times with uniform and unerring success in the 

 laboratory of this Institution, on the evening of the third instant, 

 before a number of gentlemen ; and it was also proved that, in- 

 dependent of such a provision, t'r.c lamp must have been ex- 

 tinguished — a fact, indeed, that even the tyro of chemistry is 

 well aware of: namely, the extinction of an ignited body when 

 enveloped by an inflamniable medium. For this purpose a me- 

 tallic wire (platinum, steel, and cojipcr were t!ie metals em- 

 ployed) coiled uj> in a spiral form was exposed to the flame, 

 close to the wick: the instrument was lighted, and, after some 

 time, the vvire, having become intensely red hot, was plunged 

 into a vessel containing coal gas. At each sudden immersion 

 the lamp was extinguished ; but on the expenditure of the gas, 

 instantaneously rekindled. 



On the fourth instant, a number of similar experiments were 

 repeated, and with results ccjually satisfactory. Different me- 

 thods of keeping the wire in the flame were tried in tlicse ex- 

 periments. That represented in fig. A (Plate 11.) was found to 

 be a very convenient arrangement. The wire was from l-25th to 

 l-30th of an inch in diameter; the diauieter of the spiral about 

 l-3d of an inch ; tbe number of revolutions in the spiral coil 7j 

 and these about l-.'K)th of an inch apart. 



When the lamp is kept well trimmed and supplied with sper- 

 maceti oil, the wire will be preserved of a temperature suffi- 

 ciently exalted to rekindle the lamp on its extinction, so that all 



the 



