ON THE AERIAL SYSTEM OF FORCING. 
155 
into shadow, and a very much improved mode of heating, which has only borrowed 
the name, while it retains little of the substance, has, in some two or three instances, 
been adopted by men of discerning intellect, to the great improvement of the pro- 
tective and forcing departments of horticulture. 
A very fair approximation to an uniformity of heat through an entire house — 
with a very great increase of generally diffusable temperature, if desirable, and at 
command — has been attained. Our direct observations led to the publication of that 
article (Page 70, No. 160) on an erection which comprised a vinery and cooler depart- 
ment. This machinery acted so well, that, while admitting defects, we can con- 
scientiously recommend it to those who intend to erect one or two small houses upon 
rigidly economised outlay : it should seem almost impossible to erect a greenhouse 
upon more safe and efficient principles, especially if, in lieu of sliding, or even 
movable front sashes, there be a number of external ventilating holes at the ground 
level, or even rather below it, made in the front, back, and end walls for the admis- 
sion of air from without : all or any of these may be left open, or be closed, as 
circumstances indicate ; but it is certain that air so admitted will never, even in the 
coldest weather, produce the comparative injury to plants which a blast dashing from 
the top, or even by front and end sashes invariably causes. 
The great principle before-named, first inculcated by Dalton, that each gas acts 
as a vacuum to every other gas, ought always to regulate the operations of all who 
erect plant-houses. It is this principle which forms the basis of the modified Pol- 
maise system ; and it, or any of its improved forms, must be made to conform to 
that principle. 
There are few persons, in this day of philosophical mechanism, who have been 
more assailed by rude aspersions than Mr. Meek, of Nutfield, in Surrey. Had 
that enthusiastic, high-minded gentleman, avoided the name of Polmaise — had he 
simply and philosophically announced his own conceptions, now carried into full 
effect, he would have been welcomed as an able exemplifier of scientific structures. 
He shall speak for himself in the following extract from the Journal of the Horti- 
cultural Society : — 
" The philosopher tells us there is a form of matter which diffuses heat with a 
rapidity unknown to any other ; and, moreover, this very instrument of diffusion is 
the object itself which we seek to heat ; thus, instead of employing a go-between, we 
heat that, at once, which it is our object to heat. We desire to heat a certain amount 
of air ; we provide the heat ; the air appropriates and diffuses it with an equality 
and speed which evidently cannot be attained by any other means. Is it any wonder, 
that a plan based on principles so natural and so philosophical, should be eminently 
successful ? that it should be cheap, as compared to any other means, in its first 
cost, and economical in its use? For the expense of diffusion is saved. What 
necessity exists of carrying heat to the air, when the air will travel to the heat ? 
What need of boilers, cisterns, stopcocks, pipes, and water, to produce and diffuse 
atmospheric heat ? Is it not certain that such means must involve waste in cost, 
