98 



true proportion (c). It might be possible, by annexing a graduated 

 circle to the keys of the stopcocks, to burn the gases in known pro- 

 portions, but the eye is able to judge of the heat with sufficient 

 accuracy by the light which is disengaged from the object of ex- 

 periment. The intensity of this is astonishing ; my laboratory, a 

 room of 25 feet square, is strongly illuminated by a globule of plati- 

 na, not exceeding , of an inch in diameter, and the phosphorescent 

 glare of some bodies, as lime and magnesia is intolerable, even 

 when the eye is defended by dark green glasses. But what is the 

 origin of this light ? we can conceive, that a solid heated in a 

 furnace, when it is surrounded by luminous objects, may receive 

 and emit this emanation at the same instant, but our obscure 

 flame, which is scarcely visible in broad day-light, is incapable of 

 affording it; (d^ shall we say with Davy, that ordinary matter may 

 Jjecome caloric, and light if its particles are put in violent motion, 

 or may we not rather suppose that caloric is under certain circum- 

 stances, perhaps by increasing its velocity, convertible into light ? 

 Is it too wild an hypothesis, to suppose, that the repulsion by 

 which these etliereal substances are projected from bodies, acts 

 only at insensible distances, and that they are radiated from solids 

 by the united energy of many particles, wliile in gases, only single 

 atoms can act on them, in consequence of their distance from 



(c) The heat is much more diminished by an excess of oxygen than of hydrogen, notwith- 

 standing the high capacity of this latter, for it burns in the air, and protects tlie blue interior 

 flame from the cold medium which surrounds it. 



fd) If a platina wire be ignited in the unmixed flame of hydrogen, this becomes much 

 brighter, a luminous atmosphere surrounds the metal in a msnner which it is not easy to 

 explain, 



