416 



PLANT-HOUSES. 



of quiescence is a bad conductor of heat, 

 but in a state of motion it is a good one. 

 To provide this circulation, an air-drain 

 should communicate between the stoke- 

 hole and the open flues in which the pipes 

 are laid. It need not communicate with 

 the external air, as it would thus draw in 

 too much cold air, particularly in frosty 

 weather, and lower the temperature in 

 the house instead of raising it. 



The furnace, stoke-hole, &c, n in sec- 

 tion, should be placed in a vault beneath 

 the centre of the house, access being 

 obtained to it by a well stair, m, covered 

 with a neat iron grating set level with 

 the surface of the walk or ground around 

 the house, and sufficiently large to allow 

 a man to enter freely. The vault should 

 also be sufficiently capacious to hold a 

 supply of coals and the refuse ashes, so 

 that a supply and clearing-out once a 

 month may be sufficient. The air ad- 

 mitted by the grating over the stair will 

 be sufficient to insure a well-regulated 

 combustion in the furnace, and also a 

 supply of moderately-heated air to cause 

 circulation of the heat from the pipes 

 within. In summer, in the case of the 

 greenhouse aquarium, a species of venti- 

 lation will take place when the ventilators 

 in the floor are kept open, which will 

 lower the temperature in hot weather 

 very considerably, and much to the bene- 

 fit of the plants ; while, in regard to the 

 tropical aquarium, the same means will 

 produce a circulation of air through the 

 structure, which will not only cause a re- 

 gular diffusion of heat through every part 

 of the house, from the floor upwards, but 

 will carry in much of those natural ele- 

 ments so necessary to plants, and with 

 which an allwise Power has furnished the 

 atmosphere in which we live. The smoke 

 from the furnace may be carried away in 

 a flue built within an outer covering or 

 drain, and laid upon an incline rising 

 from the furnace to the chimney-top, 

 which may be concealed behind shrubs ; 

 or it may be discharged through a vase 

 on an elevated pedestal, the smoke being 

 consumed to a great extent by some 

 of the plans recommended in Section 

 Furnaces. 



Ventilation is to be effected by open- 

 ings in the side-walls o o, and regulated 

 by brass registers placed level with the 

 floor of the passages next the front of the 



house, 6 feet apart, and 12 inches in dia- 

 meter, every alternate one communicat- 

 ing with the principal passage by passing 

 under the two outer tanks. Thus bottom 

 ventilation is amply provided for; but 

 in all circular-roofed houses with fixed 

 roofs, which such a structure as this neces- 

 sarily is, there has always been a difficulty 

 in effecting top ventilation. We propose 

 in this case that the roof be tied together 

 at d, all the astragals being fixed into a 

 circular girder, and that the part above 

 that (e) be in one piece, as shown in fig. 

 570, and attached to an upright circular 

 iron column 3 inches in diameter, formed 

 upon the telescope principle, or like a 

 common sliding pencil-case. This column 

 is to be attached to the circular girder at 

 top, and made to pass through the centre 

 tank to the stoke-hole beneath, and there 

 secured to the roof of the chamber, but 

 extending 2 feet below that roof. The 

 movable column within the outer one is 

 to be attached by four arms to the top 

 piece of the roof above d, and, passing 

 upwards to its apex, is secured to it there 

 also. A simple lever is attached to this 

 movable column at its lower end, and, by 

 elevating or depressing this lever, the 

 movable column is acted upon, and moves 

 upwards or downwards as required. From 

 _. _ n this it will be 



" 711 seen that, up- 



on depress- 

 ing the lever 

 (whose ful- 

 crum is sus- 

 pended from 

 the roof of 

 the stoke- 

 hole) the mo- 

 vable column 

 will be elevated, and consequently lift 

 up that piece of the roof e above d to 

 any height — say 6 inches — which will 

 give as much ventilation as if it were 

 removed altogether. A counter action 

 of the lever will lower this part of the 

 roof to its original place, and, being 

 made fast to the movable column, it is 

 kept in its place as securely as if it 

 were part of the roof. A common rack 

 and pinion would effect the same thing, 

 but we think the lever the simplest of the 

 two. There are various ways by which 

 the top part of such a house could be 

 elevated; we may state a very simple 



