MANAGEMENT OF THE ATMOSPHERE. 



289 



longer period, than a larger portion, when the temperature of the 

 house has increased ten or twelve degrees higher. Again, if 

 the top sashes be opened first, which is generally done, then a 

 much larger quantity of oxygen and aqueous vapor is carried 

 off than at any other period of the day. We believe it is the 

 practice of nineteen out of every twenty gardeners, to open the 

 top sashes first; then, when the internal temperature rises, and 

 more external air is necessary, the top sashes are opened still 

 more ; and, last of all, the front sashes are opened to make a cir- 

 culation; — a circulation, indeed! By the time the front sashes 

 are opened, the two atmospheres are generally equalized. Now, 

 I would ask, how is this circulation produced, and what are its 

 effects ? Not by the superior density of either atmosphere, for 

 both are the same, but by currents of wind, and draughts created 

 by other causes ; and their effect is to carry off the moisture 

 already too much reduced. The annexed figure represents a 



Fig. 57. 



method of admitting fresh air into a house which obviates the 

 evil here complained of. The air enters through the side-walls 

 at a a, then passes along beneath the floor, and enters the house 

 in the centre of the floor, at b. In this instance, no air is 

 admitted at the top; hence, the air, passing through these drains, 

 enters the house at a higher temperature than if admitted at 

 the sides or top, and, becoming gradually warmed as it ascends 

 through the aperture in the floor, rises until it is again cooled by 

 action of the external air upon the glass, then falls towards both 

 sides of the house, producing a motion somewhat similar to thar 



