810 Description of a Ventilator 
a female screw at//, adapted to the male screw c c , on 
the nosle Fig* 2, and may then be inserted into the head 
of the pipe Fig. 5, This will add to the expense ; but, in 
a large apparatus, is to be preferred, as a more certain 
security from lapse of air, than the junction of the tube 
Fig. 4, to the neck e e in Fig. 2. 
N. B. ee is a neck of wood, making a part of the hot- 
J tom Fig. 2 , whereon to secure the tube Fig. % when ap- 
plied to the nosle. The joints of the pipes, when put to- 
gether for use, should be made air-tight, by means of 
bees-wax or some stronger cement, till they reach the 
bottom of the vessel, when there is no further need of 
this precaution. The horizontal pipes should run by the 
side of the kelson the whole length of the hold. The tin 
plates of which K is made, should be punched in holes, 
like the rose of a watering-pot, in two or three lines only 
at most, and then formed into a tube, with the rough side 
outwards. L may have four or five lines of the like per- 
forations. M, and the rest, should gradually increase in 
their number as they advance towards the middle of the 
hold, and continue fully perforated to the last pipe, 
which should be closed at its end to prevent the ingress 
of the corn. It is the centre of the cargo which most re- 
quires ventilating, yet air should pervade the whole. 
Like the trade-winds, it will direct its course to the part 
most heated, and, having effected its salutary purpose 
there, will disperse itself to refresh the mass. 
Where the hatches are close-caulked, to prevent the 
influx of water, vent-holes may be bored in convenient 
parts of the deck, to be bunged up and opened occasion- 
ally, from whence the state of the corn may be known 
by the effluvia which ascend when the ventilator is work 
ing. 
The power of the ventilator is determined by the 
■square of its diameter multiplied into the length of the 
