HART VENTILATION. 
37 
Contrast the Spanish system with ours. They have a shaded 
open court yard admirably suited for creating a rising whirl- 
pool of air and they have a deliciously cool shaded retreat, within 
a roof secured from the heat of the sun. 
Dwellings in Trinidad have none or but few roof openings, 
as a rule ; they have but the shade of outside galleries, and 
the roofs are constructed with the heat attracting black slate 
which is closely nailed to the lathed or close boarded rafter 
frame, without a particle of ventilation, or in some cases, but a 
very poor attempt at it. 
I said in describing the Spanish court yard, that it created 
a “whirlpool of air.” This may be rather a curious expression 
but it is the best which I can think of. There is certainly in 
these places a whirl-pool or cyclone of ascending air and I think 
I may say without contradiction that this is the best form of 
tropical ventilation, namely, that which is created by a gentle, 
though rapidly ascending current of air — formed by a circling 
motion. If we observe carefully in our daily walks we shall find 
in the tropics that such currents are common out-door occur- 
rences, and I am of opinion that the nearer we can imitate them 
artificially for the ventilation of our homes, the greater comfort 
we shall attain. 
The reason of the creation of these currents will probably be 
given by some lecturer later on when treating on Physics or on 
Meteorology ; but I shall not attempt it to-night— but will con- 
clude with giving you my ideal of a house ventilated for use as a 
habitation in a tropical climate* — ventilation as shown in the 
Stevenson’s screens shows how a fail' estimate of the outside tem- 
perature of the air can be obtained. 
This screen, although by no means perfect, has been almost 
generally adopted by Meteorologists, as the best extant ; and 
*Here the author described a house with a roof opening at the top 
with spiral mechanical ventilations and double roof and drew a sketch on 
the blackboard. 
