154 
ON THE AEKIAL SYSTEM OF FORCING. 
In our last article upon the equable diffusion of heat in plant-houses an 
attempt was made to show that almost every species of machinery in use, and each 
attempt to modify or improve the same, had been erected and regulated upon 
erroneous principles. We have two important, paramount objects in view — economy 
of money and fuel, and the utmost attainable equability of temperature within the 
area of the building. There is no desire to interfere with the views of the opulent : 
we perceive the very extensive desire that exists among persons of limited property 
to cultivate and protect the plants which they admire ; and therefore, if it be 
possible, we would enable the amateur to possess himself of the best appliances at 
the least possible outlay. 
Fuel of any description can but afford a certain quantity of heat ; and if we even 
admit, that, by any possibility, the whole inflammable matter of a combustible be 
absolutely consumed, so as to give forth its heat, it still may happen that a major 
part of the heating power will never enter into the atmosphere of a house. A very 
few months have elapsed since it was proved by one of our philosophical lecturers 
that when coke, charcoal, and particularly pit coal, is burned in stoves of common 
form, the coal itself that lies above the portion that is in a state of actual combustion is in 
part dissolved, and carried into the chimney in the state of carbonic oxide, an inflam- 
mable gas which, under other circumstances, would take fire, give out its heat, and 
be itself converted to carbonic acid ; a gas which is the result of complete combustion, 
and in itself capable of extinguishing fire or flame with the utmost rapidity. The 
cylindrical, double-cased, hot-water boilers not long since so much in vogue, yield 
demonstrative proof of the distillation of unconsumed fuel ; for at the very time when 
the coke immediately above the bars is, to the height of four or five inches, in a 
state of active red heat, the cooler fuel above, recently supplied, shall appear quiet 
and inactive till atmospheric air from above is admitted, by removing the cast-iron 
air-tight cover which secures the summit of the inner cylinder, when an explosive 
puff of pale-blue tinted flame will rush through the cylinder, to a height that might 
seriously injure the incautious operator when examining the state of the fuel. This 
circumstance alone, connected as it is with the loss of so much inflammable matter, 
ought to disqualify these dangerous boilers. 
Since the announcement of the Polmaise system, with its paraphernalia of hot 
plates and wet blankets, the writer has had occasion to inspect some erections, and 
to bestow observation upon multitudinous articles on the merits and defects of the 
so-called system. The result is, that attempts to prove too much on the one side, 
and virulent abuse, replete with disgraceful falsity on the other, have thrown dust 
into the eyes of the sincere inquirer after truth, and equally retarded the progress 
onward toward the right path. But all this while the original Polmaise has passed 
