HORTICULTURAL JOURNAL. 251 



cessantly presented to it, and the operation of abstraction may be facili- 

 tated ; while, on the contrary, if the air is stagnant, the absorption of 

 carbonic acid may be much slower. In an absolutely still air, perspiration 

 will be reduced to its minimum, and it will increase within certain limits, in pro- 

 portion to the quickness with which the air sweeps over it. The motion of the 

 air being thus favorable to the two great operations of feeding and perspiring, 

 we shall find it is equally needed day and night, for perspiration goes on 

 principally during daylight, and feeding in the hours of darkness. A good 

 system of aeration must then be constantly in action." (Gardeners' 

 Chronicle, volume 1845, page 267.) 



With the view of effecting this, a variety of plans have been devised 

 from time to time, which, to a certain extent, have answered the purpose ; 

 but I think it will be admitted that a great deal yet remains to be done 

 before it can be said that a proper system of aeration has been perfected. 

 At present it is a desideratum, and the oftener the subject is discussed the 

 more likely are we to discover the path that shall lead us to the object 

 which has so long evaded our pursuit. 



Some years ago a correspondent suggested that a small machine, made 

 on the principle of a winnowing-fan, might be employed for the purpose of 

 ventilating hot-houses. The farmer, it was said, obtained a very powerful 

 current of air in a small compass by such means ; and the gardener, it was 

 thought, might obtain the same advantages by adopting a somewhat similar 

 plan for his forcing-houses. The machine might be so constructed as to be 

 wound up like a clock, when its gradual action would produce a gentle and 

 continuous breeze ; and, by turning a winch or handle, the degree of wind 

 might be increased to any extent desired. Such an apparatus, I find, was 

 lately made the subject of a patent. It is known as Haig's pneumatic 

 engine, and is stated to be admirably adapted for the complete ventilation 

 of houses, churches, and public buildings of every description ; the lower 

 decks and holds of ships, and the engine-rooms and stoke-holes of steam 

 vessels. It is now in use on board of her Majesty's ships Asia, Prince 

 Regent, Duke of Wellington, and several others ; and has been fitted up 

 by order of the emigration commissioners on board the Calabar, bound to 

 Port Philip. Some idea of its power may be formed from the fact that in 

 a trial that was made of it at Messrs. Hoare & Co.'s Brewery, East Smith- 

 field, one of their largest vats (which holds about 1200 barrels) was emptied 

 from carbonic acid gas in the space of 50 minutes, so that a man went to 

 the bottom of it in perfect safety. 



