274 METHODS OF VENTILATION. 



liar to itself. It is true, the elements of the atmosphere may be 

 nearly the same in one place as in another ; but they are influ- 

 enced by various circumstances, in different localities, and hold 

 soluble matters in suspension in very different proportions ; and 

 in places much screened by trees, buildings, and similar objects 

 of shelter and obstruction, air may be admitted with greater 

 impunity than in situations exposed to wind from every quarter 

 of the compass, the latter condition, as a matter of course, re- 

 quiring more care, not only in the adjustment of the apertures 

 of admission, but also in the admission itself. The course of 

 the current of air, by the common methods of ventilation, that 

 is, by opening the front, and letting down the top sashes, is ex- 

 ceedingly variable ; sometimes the actual motion created in the 

 atmosphere is little more than a foot, or fourteen inches, below 

 the surface of the glass. This motion can be easily determined 

 by holding the flame of a candle in the current, when the flame 

 will incline towards the aperture of egress ; lower it gradually 

 down, till it assumes and maintains a perpendicular position, 

 being no longer affected by the current, the volume of air being, 

 in fact, stationary, except there be some aperture of ingress else- 

 where. We have found this simple operation exceedingly useful 

 in determining the currents of air in large houses, and, in most 

 cases, it seldom fails in giving an accurate indication of their 

 course. 



However desirable a motion may be in the atmosphere of a 

 hot-house, and I do not doubt but it is beneficial, yet it is not 

 necessary that we should run headlong either upon Scylla or 

 Charybdis. There is a great difference between a motion in 

 the atmosphere created by the warm particles ascending, and 

 being replaced by the denser and colder air, and that created by 

 a tornado sweeping through the house. The former motion is 

 only perceptible to the eye of the attentive and experienced cul- 

 tivator, and he can tell at a glance, by the quivering of the 

 leaves, that they are fanned by a gentle zephyr. I am aware 

 that some gardeners have a peculiar fancy for seeing their plants 

 and vine-leaves bristling about by a good wind, and may be 

 very successful, too, in their productions; but it cannot be as- 

 serted that it is compatible with a high state of gardening skill, 



