H, Skey. — Smokeless and Self-feed inc/ Furnace. 29 



then, in four minutes, it sank to 64'', and in six minutes to 63°. This indicates 

 a loss of heat corresponding to only 14° F. by the interposition of the sheet of 

 oxidized iron. This material was proved to heat very rajjidly, and it also cools 

 rapidly if a current of cooler air is passed over it. 



From these considerations it is evident that tlie heat in the flattened 

 tubes BB is continually radiating as long as there is a current of cooler air 

 flowing through the other tube aa. Let us assume that the gases in both 

 tubes are similar in quantity and properties, then it follows that all the air 

 required by the furnace can be formed into a hot blast, having a temperature 

 of at least 300° F. This is on the assumption that the fresh air is made no 

 hotter than it would be if actually mixed with all the evolved gases ; but it 

 "will be seen that, by a proper arrangement and selection of material for the 

 tubes, the air will have been raised to nearly 300° when it has traversed 

 only half the length of the tube, or at A^ ; consequently, as it goes onward to a 

 still hotter part, near the tube B, it is continually acquiring fresh accessions of 

 heat until it reaches that part of the thermo-con vector whei-e the temperature 

 is, as we have seen, 600° ; and similarly it may be shown that the evolved 

 gases are cooled down to near 300° when they i-each B^, and as they pass on 

 they are rapidly cooled by imparting heat to the incoming current of cooler air. 

 In the above apparatus, conduction and surface radiation only are alluded to ; 

 but let us consider if transmission through a diathermanous medium could not 

 be employed to advantage. We are indebted to Melloni for the discovery of 

 the almost perfect transparency of rock-salt for all kinds of radiant heat. It, 

 moreover, does not appear to sufier by a heat approaching to redness. I am 

 unable to ascertain if there is any difliculty in procuring it in large pieces, but 

 as optical perfection would not be necessary, and plenty can doubtless be 

 procured sufficiently transparent, small panes of this substance could be 

 inserted at the top of each convolution of the air tube A. Then the hot gases 

 from the furnace will instantaneously radiate heat into the air tube, and 

 because the heat rays impinge on the surface of the sheet of oxidized iron at 

 the bottom of the air tube, therefore they are immediately arrested and impart 

 their vibrations to the contents of the air tube. Thus, as glass in our 

 ■windows transmits all the rays of light, so do these plates of rock-salt form, 

 ot doors only, but windows for radiant heat. 



It is necessary for us now to consider the radiative property of the evolved 

 gases in b, and the absorbent property of the air in the tube A (premising that 

 both these properties are always possessed equally by the same body). Fii'st, 

 "with reference to the evolved gases, Tyndall has shown that they possess these 

 qualities in an eminent degree, because they are compound gases ; but this 

 cannot be said of the air in the other tube ; indeed, if this air was quite dry 

 and jture, all the radiant heat would merely pass through it without heating it at 



