294 



VENTILATION. 



seen urged in the opposite direction by 

 the egress of warm air from the hot into 

 the cold, the action continuing until an 

 equilibrium is established in the air of 

 both rooms, which can only be the case 

 when both acquire an equal temperature. 



" The benefit to be derived from the 

 above principle may be approximately 

 calculated in the case of a vinery, or 

 rather forcing-house. Supposing the room 

 to contain as many cubic feet of air as is 

 contained in the vinery with which it is 

 in communication — say 6000 cubic feet ; 

 supposing, also, that by sun heat the 

 air in the vinery rises as much above 70° 

 as will be sufficient to render the whole 

 of the air in both compartments of 

 that temperature, and that the cold at 

 night would reduce the 6000 feet of air 

 under glass from 70° to 40° it follows 

 that 12,000 cubic feet, the quantity of 

 air in both compartments, will only be 

 reduced half as much — that is, to 55°. 

 Again, if the air in a greenhouse were 

 liable to be cooled down from 50° to 30°, 

 then in communication with a quantity 

 of air equal to that contained in the 

 greenhouse alone, and to be also reduced 

 from 50°, the minimum of the greenhouse 

 would be 40° instead of 30° ; and thus, 

 without fire heat, the plants would be 

 in a comfortable medium. In practice, 

 however, it will be doubtless found that 

 the minimum will be somewhat lower 

 than is indicated by the above calcula- 

 tions, because the inertia of the air inter- 

 feres with the otherwise free circulation 

 between the respective compartments." 



The above illustrates a very good mode 

 of ventilation, founded upon correct 

 principles, and leads us to the conclusion 

 that ventilation might be most efficiently 

 effected by constructing chambers behind 

 hothouses for the express purpose. 



Another mode of mechanically ven- 

 tilating hothouses is described by Mr 

 Walton, in " Gardeners' Journal," and is 

 to the following effect, the chief object 

 being to get rid of the unsightly appear- 

 ance of ropes, &c. hanging from the roof. 

 Fig. 398—" By this plan, both front and 

 back ventilators may be opened with 

 the tenth part of the trouble usually 

 incurred," and at the same time. " The 

 plan is very simple, consisting of a rod a, 

 which extends along the front of the 

 house, and is turned by a small windlass 



outside, at one end. This rod, or axle, 

 is attached to each of the front sashes by 



Fig. 398. 



the arm b, having a joint at its centre — 

 so that when the axle is turned in one 

 direction, this arm b opens towards the 

 straight, pushing the bottom of the sash 

 outwards; a contrary turn causes the 

 arm to collapse or fold up, and in so doing 

 draws in the sash to its original position. 

 To the extremity of the front rod a, where 

 the windlass is attached to it, is fixed a 

 cord or chain c, running up from the front 

 and along a groove in the end rafter, 

 to the top of the back wall, where it 

 passes over a pulley attached to the 

 rod or axle a, extending along the back. 

 To this axle, a, are attached small 

 rods /, one to each ventilator, the rod 

 and ventilator being connected by a 

 cord h. When the windlass turns the 

 rod a, it will, by the action exerted upon 

 the chain c, also turn the rod a, which 

 will open all the back ventilators simul- 

 taneously with the front ones. To secure 

 the proper acting of the apparatus, due 

 attention should be paid to the length of 

 the joints b and /, which must be so 

 determined, that one quarter of a revo- 

 lution of the rod will open the venti- 

 lators to their full extent. To gain 

 mechanical power, cog-wheels should be 

 used along with the windlass." This is 

 an ingenious mode of ventilation, though 

 rather complicated. The use of ropes 

 acting in conjunction with iron rods is 

 very objectionable, on account of their 

 liability to elongate or contract in certain 

 states of the atmosphere. There is no 

 reason why iron rods may not be used 

 altogether. 

 Amongst ventilating contrivances prin- 



