662 Report on the Trials of Implements at Reading. 
been tested when at work on their stacks, as neither the trials with the fan- 
cases, closed or open, can possibly represent the same conditions as would 
then exist, and conseqiieutly calculations founded on the dyuamonietrical 
figures might be misleading, so far as the stack-drying trials themselves are 
concerned. 
On the stacks the powers required would generally be intennediate between 
those with the fans " open " and " closed," but very much would depend 
upon the density and size of the stacks, sizes of air-channels, &c., and with 
such machines very slight changes of speed and lubrication may immensely 
affect the powers required. 
With regard to the remark that some fans require most power with the 
fan-cases open and others with them closed, that is quite to be understood 
from a mechanical point of view, and depends on the shape and confor- 
mation of the fans and the direction of the blades, whether radial, inclined, or 
curved. 
There are no reliable experiments analysing this interesting question 
as regards fans for air, but it is generally known that a wdl-designed air 
fan requires more power to work it open, either against the atmospheric 
pressure, or against a moderate pressure in excess of the atmosphere, than 
when closed, to prevent any transmission of air through it. Some fans, 
however, with blades of an objectionable shape, probably require more power 
to work them closed ; and the same phenomenon in others may be attributed 
to their being so placed in their cases as to admit of a churning of the air 
round and round within the case when working closed, and so corresponding 
to a transmission of air under more or less pressure. 
Fans for water are better understood, but the same mechanical laws apply 
in both cases; and it is worthy of remark that a well-designed centrifugal 
pump working with closed outlet under a pressure of 10 ft., requires scarcely 
any power to work it, while the same pump discharging with an open 
outlet at the same height, will take a considerable power, possibly even live 
or ten times as much as before. 
It will be observed that the fans were (1) tested with inlet 
closed for the purpose of observing " the difference of pressure in 
inches of water maintained " (cols. 5 and 6), and (2) with inlet 
open, when the velocity of the flow of air was observed. 
Perhaps the most marked feature of these trials is the great 
increase of pressure, as shown by the water-gauge, obtained by 
an increased velocity of the fan. It will be seen that Bamlett's 
fan, when worked at 700 revolutions per minute, displaced only 
•1 inch of water, while 1050 revolutions displaced •? inch, and 
2100 gave 2'9 inches as the result. It may be noted here 
that 1050 revolutions can be got by 60 turns of the handle 
per minute, and that one man can without difficulty maintain 
this speed for a good while. It would be easy, by an inter- 
mediate motion, to double the velocity of the fan, and two men 
could then work it and obtain four times the result which one 
man now gets. 
Phillips's hand fan was tested at 40 and 60 turns of the 
handle per minute, giving respectively 400 and 600 fan revo- 
lutions. The first speed represented what the Judges thought 
one man woidd do. The higher speed what Mr. Phillips's 
