356 WRITINGS OP JOSEPH HENRY. [1855 



composed of fire-brick and heated red liot, they throw off into 

 the room more heat than the burning coals themselves." 



"The fuel therefore," says Count Rumford, "should be 

 disposed or placed so as to heat the back and sides of the 

 grate, which must always be constructed of fire-brick and 

 never of iron." 



The vertical stratum of coal should be as thin as is consist- 

 ent with perfect combustion, for a large mass of coal in the 

 grate arrests the rays which proceed from the back and sides 

 of the grate, and prevents their coming into the room. The 

 grate or fire-place itself may be so contrived as to produce a 

 proper degree of radiation, but when this is not the case, 

 Rumford advises that the bottom of the grate be covered with 

 a single layer of balls of fire-brick, each perfectly globular 

 and two and a half or two and three quarters inches in di- 

 ameter. " On this layer of balls fire is to be kindled, and 

 in filling the grate more balls are to be added with the coals, 

 care being taken to mix the coals and balls well together in 

 due proportions. If this is done the fire will not only be 

 very beautiful, but will send off a much greater quantity of 

 radiant heat into the room than without them." Rumford 

 also declares that these balls cause the cinders to be almost 

 entirely consumed. "The same effect is said to be produced 

 by the mixture of coals and clay when the fuel is burnt in a 

 a close fire-place, such as an iron stove; and it is the custom 

 in the Netherlands to mix moistened clay with the coals 

 before they are introduced into a stove of this form." 



Count Rumford gives no account, in the paper I have cited, 

 of experiments by which the fact of the greater radiation 

 from the balls was tested. 



In reading his paper some years since the idea occurred to 

 me that this experiment would be worthy of repetition, with 

 the more manageable and delicate appliances which science 

 has of late years furnished for the use of the investigator. 

 For this purpose I employed the thermo-electrical apparatus 

 of Melloni, furnished with a tube like a telescope to circum- 

 scribe the field of radiation, and the result confirmed the 

 statement of Rumford that more heat was radiated from 



