of Ventilating and Warming Buildings. S6T 
ciple w€ have already considered. It has already been remark- 
ed, that, in employing the cockle, we obtain only a very limited 
surface for affording heat ; but to render the small surface it af- 
fords as eflPective as possible, Messrs Strutt have contrived a 
most ingenious method of causing the air to be projected in 
small streams with considerable velocity against the hottest part 
of the cockle ; and, again, that air can only ascend into the air- 
chamber which has been brought into close contact with the 
heating surface on the upper part of the cockle. 
The method of warming by the cockle is rather more limited 
in application than that by slow conductors ; as, in order to get 
power to move the air through with sufficient velocity, the cockle 
must be at about the depth of twenty feet below the rooms it is 
intended to warm. 
I have considered the cockle as a means of affording heat a 
little out of its place as an invention, for it was preceded by an- 
other, and more safe and convenient mode of distributing heat’ 
I allude to Steam, which was first proposed by Colonel William 
Cook, in the Philosophical Transactions for 1745 ; but it does 
not appear to have been much used till after its application to 
cotton *mills at Glasgow in 1799- 
The value of steam, as a vehicle for distributing heat, con- 
sists in the facility with which it can be conveyed from one fire 
to any part of the buildings to be warmed, — in the temperature 
of the surface affording heat never exceeding that degree which 
is injurious to the air, — and in the perfect safety from fire. 
Low pressure steam should always be employed for distributing 
heat, for when the just proportion of heating surface is prepared, 
the increased temperature of high pressure steam is not wanted ; 
and it may be proved, that there is no economy in using it, 
while it must be dangerous in proportion to the pressure it is 
worked at ; for it cannot be expected that an experienced en- 
gineer will be employed in attending the boiler of an apparatus 
for warming a building. But employing a simple apparatus, 
and low pressure steam, with a species of safety-valve inaccessible 
to the attendant of the fire, and yet not likely to be out of order, 
will render a steam apparatus perfectly safe, and capable of pro- 
ducing the greatest effect from a given quantity of fuel. 
The boiler for producing steam is usually constructed in the 
