II ART VENT! L ATI OX. 
35 
cone of heated air which is so often boxed up in the apex of the 
roof like the heated salamander of a French cook over an omelet. 
That roofs closed at the apex arc not suited to tropical 
climates, can also be readily proved. 
The Horticulturist who deals with structures which are 
partly heated by artificial means, and partly by the sun, has to 
provide means whereby be can regulate the temperature within 
one or two degrees Fahrenheit, notwithstanding a sudden outburst 
of the sun, perhaps on a clouded day, when he has had to keep 
his heating apparatus going to maintain the temperature ; which 
outburst would without ventilation result in a rapid rise of 
temperature. To obviate this difficulty he has to have resource 
to ventilation, which he first affords, where ? At the base of his 
building, “Oh, no ! his thermometer tells him better V He first 
allows the heated air to escape, and makes at the same time 
provision for the admission of cooler air by establishing a gentle 
downward current. Affording an outlet to the heated air at the 
apex of the roof causes but little draught (as great a danger to 
the health of plants as to that of animals) but only so much as 
can be drawn in by the openings afforded in the lower part of the 
house — or by the counter downward current of cool air which is 
sure to enter by the opening at the top of the roof. 
Ventilation, by its. allowing a passage of air and causing 
evaporation, produces a cooling effect upon the atmosphere of a 
dwelling — but any direct ventilation which causes a strong current, 
of air through a room in one direction is to he avoided as danger- 
ous as it abstracts too great an amount of heat from uncovered or 
covered parts of the body, or surface of plants, and is apt to cause 
the individual who sits in such a position to “ take cold” and the 
plant to he what Horticulturists call “ chilled.” If therefore we 
are not to use such currents, what is the next best thing to do. 
Such currents we know are quite too common, being the result 
of construction being left to persons unacquainted with the 
first principles of ventilation. 
