Q04 W H E 
in which case it is thought best for the wheel 
to be dished, because the spokes become 
perpendicular in the rut, and therefore have 
the greatest • strength when the obliquity of 
the road throws most of the weight upon 
tne'm ; whilst those on the high ground have 
less weight to bear, and therefore need not 
be at their fail strength. 
4. The axles of the wheels should be quite 
straight, and perpendicular to the shafts, or 
to the poie. When the axles are straight, 
the rims of the wheels will be parallel to each 
other, in which case they will move the 
easiest, because they will be at liberty to pro- 
ceed straight forwards. But in the usual way 
ol practice, the ends of the axles are bent 
downwards, which always keeps the sides of 
the wheels that are next the ground nearer to 
one another than their upper sides are ; and 
this not only makes the .wheels drag sideways 
as they go along, and gives the load a much 
greater power of crushing them than when 
they are parallel to each other, but also en- 
dangers the overturning the carriage when a 
wheel falls into a hole or rut, or when the 
carriage goes on a road that has one side 
lower than the other, as along the side of a 
hill. 
5. Large wheels are found more advan- 
tageous for rolling than small ones, both with 
regard to their power as a longer lever, and 
to the degree of friction, and to the advantage 
in getting over holes, rubs, and stones, &c. 
If we consider wheels with regard to the fric- 
tion upon their axles, it is evident that small 
wheels, by turning oftener round, and swifter 
about the axles, than large ones, must have 
more friction. Again, if we consider wheels 
as they sink into holes or soft earth, the large 
wheels, by sinking less, must be more easily 
drawn out of them, as well as over stones and 
obstacles, from their greater length of lever 
or spokes. 
It is a fact, however, that the draught ought 
not to be horizontal, but rather inclined: be- 
cause in the horizontal draught the collar 
presses against the chest of the horse, instead 
of bearing on his shoulders, as in an inclined 
draught; and because in this latter circum- 
stance the wheels pass more easily over ob- 
stacles than when the draught is horizontal. 
Hence it appears, that wheels are the more 
advantageous as they are larger, provided 
they are not so high as to make the draught 
horizontal ; and when they are very large 
also, they become too heavy; or if they are 
made light, their strength is proportionally 
diminished, and the length of the spokes 
renders them more liable to break ; besides, 
horses applied to such wheels would not be 
capable of excising their utmost strength, 
for the reasons already assigned, small wheels 
occasioning the horses to draw upwards. 
6. Carriages with four wheels, as waggons 
or coaches, are much more advantageous 
than carriages with two wheels, as carls and 
chaises ; for with two wheels it is plain the 
tiller-horse carries part of the weight, in one 
way or other; in going down hill, the weight 
"bears upon the horse ; and in going up hill, 
the weight falls the other way, and lilts the 
horse, which is still worse. Resides, as the 
wheels sink into the hole: in the roads, some- 
times on one side, sometimes on the other, 
the shafts strike against the tiller’s sides, 
which destroys many horses : moreover, when 
jone of the wheels sinks into a hoie or rut, half 
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the weight falls that way, which endangers 
the overturning of the carriage. ‘ 
7. It would be much more advantageous to 
make the four wheels ol a coach or waggon 
nearly of a height, than to make the tore- 
wheels of only half the diameter of the hind- 
wheels, as is used in many places. The fore- 
wheels have commonly been made of a less 
size than the hind ones,, both on account of 
turning short, and to avoid cutting the braces. 
Crane-necks have also been invented for 
turning yet shorter; and the fore-v heels have 
been lowered, so as to go quite under the bend 
of the crane-neck. 
When a horse draws hard, it is observed 
that he bends forward, and brings his breast 
near the ground, and then if the wheels are 
high, he is pulling the carriage against the 
ground. A horse tackled in a waggon will 
draw two or three ton, because the point or 
line ot traction is below his breast, by the 
lowness ot the wheels. It is also common to 
see, when one horse is drawing a heavy load, 
especially up hill, his fore-feet will rise from 
the ground; in which case it is usual to add 
a weight on his back, to keep his fore-part 
down, by a person mounting on his back or 
shoulders, which will enable him to draw that 
load which he could not move before. The 
greatest stress, or main business of drawing, 
is to overcome obstacles ; for on level plains 
the drawing is but little, and then the horse’s 
back need be pressed but with a small weight. 
8. The utility of broad wheels, in amend- 
ing and preserving the roads, has been so 
generally believed, as to have occasioned the 
legislature to enforce their use. At the same 
time, the proprietors and drivers of carriages 
seem to be convinced by experience, that a 
narrow-wheeled carriage is more easily and 
speedily drawn by the same number of 
horses, than a broacl-wheeled one of the same 
burthen ; probably because they are much 
lighter, and have less friction on the axle; 
and the owners of broad -wheeled waggons 
contrive in general to make them as destruc- 
tive to roads as narrow-wheeled ones, by 
making the rim of the wheel of unequal dia- 
meters, and the waggon consequently to go 
generally on a sharp and narrow edge. 
Wheel-animals, brachionus, a genus of 
animalcules which have an apparatus of arms 
for taking their prey. T|ps apparatus has 
been supposed, by microscopical writers, to 
be a kind of wheels ; and they thence named 
the creatures that are possessed of it, wheel- 
animals. 
WHIRLPOOL, an eddy, vortex, or 
gulph, where the water is continually turning 
round. These in rivdrs are very common, 
from various accidents, and are usually very 
trivial, and of little consequence. In the sea 
they are more rare, but more dangerous. 
Sibbald has related the effects of a very re- 
markable marine whirlpool among the Or- 
cades, which would prove very dangerous to 
strangers, though it is of no consequence to 
the people who are used to it. This is not 
fixed to any particular place, but appears in 
various parts of the limits of the sea among 
those islands. Wherever it appears, it is very 
furious; and boats, &c. would inevitably be 
drawn in and perish with it ; but tire people 
"ho navigate them are prepared for it, and 
always carry an empty vessel, a log of wood, 
or large bundle of straw, or some such thing, 
in the boat vvitli them ; as soon as they per- 
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ceive the whirlpool, they toss this within its 
vortex, keeping themselves out ; this sub- 
stance, whatever it may be, is immediately 
received into the centre, and carried under 
water; and as soon as this is done, the sur- 
face of the place where the whirlpool was be- 
comes mooth, and they row over it with 
safety; and in about an hour they see the 
vortex begin again in some other place, usu- 
ally at about a mile distance from the first. 
WHIRLWIND. This phenomenon is 
well defined by its name. Its nature mav be 
illustrated by recun »ng to the same kind of 
motion in a denser fluid. When water is 
flowing through an aperture in the bottom of 
a vessel, we may observe that the meeting of 
the currents which proceed from all sides to- 
wards the opening, gives rise at length to a 
circular motion just over it: at first confined 
to a small space, but spreading bv degrees, 
until it occupies a large portion of the sur- 
rounding water. At this time, the centrifugal 
force becoming greater every instant, the 
water absolutely quits the central space, leav- 
ing a hole through it, which, together with 
the whirling motion, continues during the re- 
maining time of the discharge. Now, as the 
water descends by its gravity, and the other 
effect depends on a lateral impulse, given by 
the most powerful of tire confluent streams, 
so the healed air, over some particular tract, 
ascending by the lateral pressure of surround- 
ing colder and heavier air, may at any time 
give rise to a whirlwind of greater or less ex- 
tent and force, according to the quantity of 
air required to: be thus transmitted to a higher 
station, in order that the equilibrium of the 
atmosphere may be restored. There is want- 
ed for this purpose only a sudden I impulse 
from some quarter, sufficient to disturb the 
uniform motion of the ascending stream. 
The effects of whirlwinds are sometimes tre- 
mendous; not only large quantities of hay, 
and other light bodies, but even the limbs of 
trees, the roofs of houses, and other pon- 
derous matters, having been lifted up and 
carried off by them. Their effects are no 
where more conspicuous than in the vast 
pillars of sand, so much dreaded by travellers, 
which they raise from the moveable surface of 
the deserts in the East, and of which we have 
a good account in Bruce’s Travels. Dr. 
Franklin, in whom sagacity of observation 
was eminently united with the power of 
simple and plain description, has left us the 
following account of a moderate whirlwind, 
of which he was an eye-witness close at hand. 
“Being in Maryland (says the, doctor) 
riding with colonel Parker, and some other 
gentlemen, to his country-seat, we saw in 
the vale below us a small whirlwind, be- 
ginning in the road, and shewing itself 
by the dust it raised and contained : it ap- 
peared in the form of a sugar-loaf, spinning 
on its point, moving up the hill towards 
us, enlarging as it came forward. When it 
passed by us, its smaller part, near the 
ground, appeared no bigger than a common 
barrel, but widening upwards, it seemed at 
40 or 50 feet high, to be 20 or 30 feet in dia- 
meter. The rest of the company stood look- 
ing after it, but my curiosity being stronger, 
I followed it, riding close by its side, and ob- 
served it licking ii]i, in its progress, all the 
dust that was under its smaller part. As it 
is a common opinion, that a shot fired through 
a water-spout will break it, .1 tried to break 
