TRANSACTIONS OP THE SECTIONS. 589 



To bring this matter to the test of experiment, he tried 

 whether the hght would continue to appear when the bodies in 

 question are heated without the contact of air. Wax, tallow, 

 and other inflammable matters were heated in different close 

 tubes in the dark ; they were observed to give out no light 

 until they were opened, when it appeared as usual. On closing 

 them again, if the heat was kept up, the light gradually disap- 

 peared, but was restored on again opening the tubes to the air. 

 A roll of paper, heated in a close tube till part was charred, 

 gave out no light, but a piece of paper applied externally to the 

 heated tube became immediately luminous. Some tallow heated 

 in a ladle till it became luminous, lost its light on being plunged 

 into carbonic acid gas. 



It having thus been proved that the absence of oxygen pre- 

 vented the appearance of the light, it was natural to expect 

 that a free supply of this element would increase it. Some wax 

 was heated in a ladle till it became luminous in the dark, and 

 on being plunged into oxygen gas it became brighter, and if 

 the heating had been considerable, although there was no 

 spark, it burst out into an open flame. Wax, lac, cocoa oil, 

 tallow, sperm oil, sulphur, and some other things could be 

 kindled into open combustion in this way ; but with paper, 

 most vegetable oils, silk, &c. the pale light was only brightened 

 by contact of oxygen. 



The author considers it, therefore, proved that the light ob- 

 served was not phosphorescence, but depended on chemical 

 action between the air and the subject of the experiment; that 

 it was, in short, a form of combustion. The bodies which give 

 out most light are wax, animal oils, hair, silk, wool, fine white 

 paper, cotton fabrics, aether vapour, olefiant gas, and sulphur. 

 Some of these, as papei', tallow, and cocoa oil, begin to give 

 out light in a dark room below 300°. Wax requires a tem- 

 perature of at least 400° ; and this, the author remarks, is the 

 reason why wax candles burn with little or no smell, whilst, in 

 those of tallow, portions near the wick are heated sufficiently 

 to undergo the imperfect combustion, which causes the odour 

 so disagreeable in an imperfectly extinguished candle. The 

 degree of heat necessary for low combustion may be estimated 

 by the fact, that as soon as oils or other compound inflamma- 

 bles begin to give out vapours, they will be found to be lumi- 

 nous in the dark. When, therefore, tallow or oil is heated to 

 ebullition in contact with the air, the surface is actually under- 

 going combustion. If the heat be further increased, the pale 

 luminosity elevates itself into a lambent flame, which, under 

 circumstances favourable for the accumulation of heat, will 



