WHE 
every revolution one turn more with re- 
spect to the surrounding objects, than it 
would make, if its centre were at rest, 
during one turn of the w’heel which is fixed; 
and this circumstance must he recollected 
when such wheels are employed in planeta- 
riums. 
Wheels are usually made of wood, of 
iron, either cast or wrought, of steel, or of 
brass. The teeth of wheels of metal are 
generally cut by means of a machine ; the 
wheel is fixed on an axis, which also carries 
a plate furnished with a variety of circles, 
divided into different numbers of equal 
parts, marked by small excavations ; these 
are brought in succession under the point of 
a spring, which holds the axis firm, while the 
intervals between the teeth are expediti- 
ously cut out by a revolving saw of steel. 
The teeth are afterwards finished Iry a file ; 
and a machine has also been invented for 
holding and working the file. It is fre- 
quently necessary in machinery to protract 
the time of application of a given force, or 
to reserve a part of it for future use. This 
is generally effected by suffering a weight to 
descend, which has been previously raised, 
or a spring to unbend itself from a state of 
forcible, flexure, as is exemplified in the 
weights and springs of clocks and watches. 
The commop kitchen jack is also employed 
for protracting and equalizing the operation 
of a weight ; in the patent jack the same 
effect is produced by an alternate motion, 
tiie axis being impelled backwards and for- 
wards, as in clocks and w'atches, by means 
of an escapement, and the place of a 
balance spring being supplied by the twist- 
ing and untwisting of a cord. 
In these machines, as well as in many 
others of greater magnitude, the fly wheel is 
a very important part, its velocity being in- 
creased by the operation of any part of the 
force which happens to be superfluous, and 
its rotatory power serving to continue tiie 
motion when the force is diminished or 
withdrawn. Thus, xthen a man turns a 
winch, he can exert twice as much force in 
some positions as in others, and a fly enables 
him in some cases to do nearly one-third 
more w’ork. In the pile engine, also, with- 
out the help of the fly, the horses would fall 
for want of a counterpoise, as soon as the 
weight is disengaged. Such a fly ought to 
be heavy, and its motion must not be too 
rapid, otherwise the resistance of the air 
will destroy too much of the motion ; but 
iu the kitchen jack, as well as in the 
striking part of a clock, where tlie super- 
WHI 
fluous force is purposely destroyed, the fly 
is made light, and strikes the air with a 
broad surface. An effect similar to that of 
a fly and a spring is sometimes produced iu 
hydraulic machines by the introduction of 
an air vessel, the air contained in which is 
compressed more or less according to the 
intensity of the force, and exerts a more 
uniform pressure in expelling the fluid 
which is forced irregularly into it. See 
Young’s Lectures. 
Wheel, in the military art, is the word 
of command when a battalion or squadron 
is to alter its front either one way or the 
other. To wheel to the right, directs the 
man in the right angle to turn very slowly, 
and every one to wheel from the left to the 
right, regarding him as their centre ; and 
vice versa when they are to wheel to the 
left. When a division of men are on the 
nrarch, if the word be to wheel to the right 
or to the left, then the right or left hand 
man keeps his ground, only turning on his 
heel, and the rest of the rank move about 
quick till they make an even line with the 
said right or left hand man. 
Wheels, water. See Mill. 
WHIRLWIND, a wind that rises sud- 
denly, is exceedingly rapid and impetuous, 
in a whirling direction, and often progres- 
sively also; but it is commonly soon spent. 
Dr. Franklin, in his Physical and Meteoro- 
logical Observations, read to the Royal 
Society in 1766, supposes a whirlwind and a 
water-spout to proceed from the same cause ; 
their only difference being, that the latter 
passes over the water, and the former over 
the land. This opinion is corroborated by 
the observations of many others, who have 
remarked the appearances and effects of 
both to be the same. They have both a 
progressive as W'ell as a circular motion; 
they usually rise after calms and great heats, 
and mostly happen in the warmer latitudes : 
the wind blows every way from a large sur- 
rounding space, both to the water-spout and 
whirlwind ; and a water-spout has, by its 
progressive motion, passed from the sea to 
the land, and produced all the phenomena 
and effects of a whirlwind ; so that there is 
no reason to doubt that they are meteors 
arising from the same geneial cause, and 
explicable upon the same princi|)les, fur- 
nished by electrical experiments and dis- 
coveries. 
WHISPERING places, are place.? where 
a whisper, or other small noise, may be 
heard from one part to another, to a great 
distance. 'I'hey depend on a principle, tliat 
