80 PRESERVATION OF FOOD BY REFRIGERATION ; 
same registration wherever it was put. This may be 
accounted for by the fact that at any place in the enclosure 
where the temperature was higher, the air would become 
more expanded and lighter and consequently a more rapid 
circulation upward would take place at that particular 
point until equilibrium was established ; and experiment 
showed that this was very quickly done. As an additional 
aid to producing the greatest amount of contact of the cold 
air with the surface of the meat and screens, it might be 
advisable to produce an artificial circulation by means of 
fans or blowers. Probably the best results would be 
obtained with fans placed on the walls near the floor and 
worked from the outside. If two sides of the room were 
fitted with these, an additional contact of the cold air 
would be produced which would be of great advantage. 
It would imitate to some extent a breeze of wind, and it is 
in everyone’s experience that any warm body placed in a 
draught is cooled more rapidly than is the case when the 
only ‘current is that produced by ie warmed air ascending 
along the surfaces of the hot body.* 
It should also be borne clearly in mind that what we are 
endeavouring to do, is to exclude the germs, which are the 
cause of putrefaction, from the meat we are operating upon. 
As these germs are present ev eryw. here, and I only require 
a temperature ranging from, say, 35° F. to 95° (being most 
active at the latter point, and practically dormant at the 
* As it may often be desirable to promote a vigorous circulation in rooms in 
which meat is hanging, a careful examination of the effect produced by the 
action of the fan becomes necessary in order that the actual amount of 
energy which is expended in driving it may be calculated, and from that the 
equivalent amount of heat ascertained which is of necessity dissipated in the 
air contained in, or passing through the room. 
From the laws governing falling bodies, and also from actual experiment, 
the exact amount of power required to drive a fan through which a certain 
amount of air at a given velocity is passing, is readily ascertained. In his 
‘Treatise on Heat,’’ Mr. Box gives the amount of air passing per minute 
through fans of various dimensions, and running at different speeds, and 
also the amount of energy in foot-pounds expended in doing the work. As 
772 foot-pounds is the dynamical equivalent of one unit of heat, the amount 
of heat evolved as the result of the motion of the fan is thus deducible. 
Taking the work of a 50,000 feet refrigerating machine, running at a 
speed of 65 revolutions per minute, the ‘amount of air actually passed 
through the compressors will be about 40,000 per hour, and if a fan be used 
to circulate this air, of tke dimensions and running at the speeds as given 
