30 Transactions.— Miscellaneous. 
all until it reached a surface formed by an absorbent body, such as our oxidized 
iron, which is capable of receiving the heat vibrations, which receptive surface 
can then heat the air above it. 
Now, as the small amount of aqueous vapour in our atmospbere is the 
main absorber of radiant heat, thus allowing the diathermanous air to become 
heated, which heated air can then be conveyed to distant parts by winds ; so 
also can a minute admixture of the compound molecules of various gases— 
such as those from coal—greatly promote the heating of air for blast furnaces. 
It is evident that in this manner the heat vibrations alone can be 
transferred from one tube to the other, while their gaseous contents are 
prevented from mixing. If a revolving fan be the means adopted for 
circulating the gases, it can be applied to any convenient part of the circuit of 
either of the tubes А or B. In the figure it is connected with A, and therefore 
first draws the fresh and heated air, and then discharges it under pressure into 
a large and broad tube extending close along the bottom of the boiler, and 
thence into a reservoir directly below the furnace and boiler, which supplies 
the £wyéres with the heated air. The thermo-convector and connections there- 
from are covered with felt, and then cased with tin, leaving an air space 
between. 
The outlet of the tube в conveys the waste and cooled gases down wards 
over a shallow vessel of water (c), thus arresting the ashes, which speedily 
Sink, and the gases can escape there for locomotives (which would be an 
important desideratum in tunnels and underground railways), or be conveyed 
over the ship's side in marine engines, or else made to go upwards through a 
funnel by the pressure of the blast. This funnel is useful in first getting up 
the fire, for which purpose the door p is lowered, which then closes the 
tube s. 
As there is a considerable amount of water in some brown coals, and as 
this would have a tendency to condense in the tube в and thus arrest the 
ashes, it was necessary to determine the temperature at which its vapour 
would eondense, and I find that if 10 per cent. of water exist in the coal, its 
vapour will not condense until it is lowered to 27? F., which gives a sufficient 
margin to ensure a dry exit to the ashes. 
lt has been shown by Joule and Mayer that the mechanical force arising 
from heating llb. of water 1° F. is equal to raising 772Ibs. one foot high. 
When we therefore consider the enormous quantity of air necessary to promote 
combustion of the fuel (one ton of coal requiring about 448,000 cubic feet, or 
more than 15 tons), and, further, that this immense volume of air requires its 
temperature raising to that of the burning fuel, it is evident that a very great 
saving can be effected by heating it before it enters the furnace, for it matters 
not on what part of the absolute scale this 1? increase occurs, let it only be 
