20 



VENTILATION AND COVERING OF HOT-HOUSES. 



One point connected with the application of these coverings 

 which I consider would constitute an improvement, and which, 

 as far as I am aware, has never been acted on, is that of having 

 them to fit so accurately as to exclude the external air (a matter 

 of no difficulty in the degree required), and then to have a series 

 of ventilators provided, to stand open during the night, whereby 

 an interchange of the atmospheric volume would take place 

 throughout the night, without exposing the plants to contact 

 with cold air. The stagnation of the internal atmosphere would 

 thus be prevented, in consequence of the interior air, and the air 

 between the glass and the covering being of different degrees of 

 density owing to their being differently charged with heat. By 

 this plan, therefore, I conceive that direct benefit would accrue 

 to the plants ; and it would also materially assist in preserving 

 that cooler — but not cold — night temperature, which the iear of 

 injury from frost prevents from being now fully realized in ordi- 

 nary cases. 



The annexed diagram represents one of the many ways in 

 which this idea might be carried into practice. It will be under- 

 stood that, as here shown, the side shutters and end shutters (the 

 latter not indicated) fit into grooves, the upper groove being 

 attached to iron pins, and thus fixed at a proper distance from 

 the building without obstructing the passage of air along the 

 enclosed space, and that on the lower side being so fixed as to 

 exclude the external air in that direction. The top or roof 

 shutters also run into a groove along the ridge of the roof, and 

 at the lower end fix close down to the top of the side shutters, 

 fastening with a button. Each of the shutters should have a 

 projecting fillet fixed on one side, so as to shut close over the 

 adjoining one. The shutters, themselves, should of course be 

 made of light frame-work, strengthened where necessary with 



