^®^51 WRITINGS OF JOSEPH HENRY. 359 



ascend, without communicating its heat to the metal. If 

 however in this case the current of air be obstructed, and the 

 cylindrical motion deranged by partially closing a damper, 

 the heat immediately around the point of obstruction will 

 be greatly increased. With a proper arrangement of parts 

 I have known a dark stove-pipe immediately to become red 

 opposite and above the damper by the partial closing of this 

 valve. It is probable that heat might be economized in cer- 

 tain cases by introducing radiating materials in flues. It 

 should however be recollected that the draft would be im- 

 peded by the introduction of foreign materials: 1st. On 

 account of a direct obstruction; and, 2nd. Because of the 

 diminished temperature. 



It is frequently stated in works on chemistry that the 

 heating power of the flame of the compound blowpipe is very 

 great, while its illuminating power is quite small. The truth 

 is however that the radiation of heat from its flame is only 

 commensurate with its radiation of light, and that what tends 

 to increase the one will also increase the other. 



The radiation from heated — though non-luminous air, 

 would, from these views, appear to be small, though from 

 meteorological considerations they would seem to be con- 

 siderable. 



That a solid substance increases the radiation of the heat 

 of a flame is an interesting fact in connection with the nature 

 of heat itself. It would seem to show that the vibrations 

 of gross matter are necessary to give sufficient intensity of 

 impulse to produce the phenomena of ordinary radiant heat. 

 Also, since the light is much increased by the same process 

 we would infer that by means of the solid the vibrations 

 constituting heat are actually converted into those which 

 produce the phenomena of light. The whole subject is 

 worthy of further investigation, both in a practical and 

 abstract scientific point of view. 



