66 



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 diffe- 

 rent 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 fear of 

 injury from frost prevents from being more fully 

 realised in ordinary cases. 



The annexed diagram represents one of the many 

 ways in which this idea might be carried into practice. 

 It will be understood 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 ef the roof, and at the lower end fix close 

 down to the top of the side shutters, fastening with a 



