W HEEL-CARRIAGE. 
salis,” says Mr. Markwick, “were always found 
deposited on the principal stem, just above the 
root. This stem it invariably destroyed, which 
gave the crop a most disastrous appearance, so 
that there was scarcely a hope of any produce; 
but after the larva had changed into a chrysalis 
state, the mischief ceased, and the root was not 
so materially injured as to prevent its throwing 
out fresh shoots on each side, and stocking it- 
self, as the farmers term it, as I experienced by 
those I planted in my garden.” Bjercander re- 
commends that the infested stems should be pull- 
ed up and burned while the insect is yet in the 
larva or pupa state; but as the plant makes such 
vigorous efforts to recover itself, and even at 
times succeeds in bringing ears to maturity, it 
| seems preferable, as Mr. Markwick advises, to 
pinch the central leaves just above the crown of 
the root, which would probably destroy the in- 
sect without materially affecting the vitality of 
the plant. It was found that it was only the 
early sown wheat that was attacked, such fields 
as were sown later than the middle of October 
escaping without injury. 
WHEAT-GRASS. See Wueat. 
WHEAT-MIDGE. See Wuear-Fty. 
WHEAT-RIDDLE. See Rippie. 
WHEEL. See Wueer-Carriace, Cart, and 
Waaaon. 
WHEEL-BARROW. See Barrow. 
WHEEL-CARRIAGE. The principal wheel- 
carriages used in British agriculture are noticed 
in the articles Cart, Waccon, and Liquip Ma- 
NURE CART; and some important topics con- 
nected with them are discussed in the articles 
Friction, Spring, Draveut, Roap, and Horsr. 
We shall, in this place, make ample extracts, 
with some slight alterations, from an able essay 
on agricultural wheel-carriages by the distin- 
guished mathematician William Galbraith, in 
the 2d and 4th Volumes of the Quarterly Jour- 
nal of Agriculture. 
Wheel-carriages are generally divided into two 
kinds or classes—one having two wheels, and the 
other four; and both these have their peculiar ad- 
vantages. For lighter purposes, those having two 
wheels are generally employed. They are more 
readily managed, quicker in their movements, and 
relatively perform a greater quantity of work with 
the same number of horses than the larger machines; 
while for the transportation of the more bulky and 
ponderous objects, those having four wheels are most 
convenient, and often absolutely necessary. The 
bodies of the carriages which are intended to contain 
the load supported upon the wheels, are, or ought 
to be, formed according to the species of loads they 
are likely to carry. When the loads are specifically 
light, the body should be large and full, so as to 
bring the centre of gravity as low as possible, to 
prevent the cart from overturning on an inclined 
road, when highly loaded with comparatively light 
materials, as hay, straw, and similar substances. 
For loads of great specific gravity in particular, that 
is, loads of considerable weight within a small bulk, 
the body of the carriage should be strong and com- 
pact, and every advantage taken of the materials of 
which it is constructed, to render it sufficiently 
711 
strong, with the least possible weight, by means of 
a proper arrangement of its parts to resist pressure 
without derangement or fracture. This can only be 
accomplished by possessing an accurate knowledge 
of the relative strains in different parts, and then 
applying the iron, wood, and other materials, in the 
best possible manner, founded upon scientific princi- 
ples. In the common cart, for example, with two 
wheels, since the shafts must support generally the 
most considerable strain in a vertical direction, they 
should therefore be stronger that way than in a hori- 
zontal direction; or asection of each shaft somewhat 
rounded in an elliptical or parabolic shape, should 
have its greatest diameter in a vertical position. 
This is obvious from the well known property of 
beams demonstrated by Galileo, that their strength 
is proportional to the breadth multiplied by the square 
of the depth. Whence the relative strength of two 
beams of the elliptical or parabolic form, supposing 
the area of the section to be the same, is as the 
longer diameter to the shorter. This shows the 
great importance of giving every part not only its 
proper size, but also its true position. No doubt 
sometimes in turning a cart, there is an additional 
strain on the shafts in a horizontal direction, though 
far from being sufficient to justify such a deviation 
from sound principles. 
The axle ought to be properly and securely fixed 
to the body of the carriage, by bolts, hoops, or such 
other means as may seem most convenient. To give 
the wheel the best position for easy motion, and as 
little friction as possible, the general shape of the 
axle should be straight. Its arms should be rounded, 
slightly tapering, in the form of a frustrum of a cone, 
and smallest at the extremities, that it may not wear 
loose; andat the same time that it may allow the 
wheel to be readily removed and replaced without 
being too tight, or having too much play, though 
sufficient to admit the usual compositions of tar, 
grease, &c., to lubricate the axle and diminish fric- 
tion. As every body is liable to bend by pressure, 
it is obvious that the axle, whether made of wood 
or iron, will be liable to flexure in a slight degree, in 
a vertical direction. Since the force of the power 
applied to move the carriage forward will be opposed 
by the friction of the wheels upon the irregularities 
of the road, there will also be a slight tendency of 
the axle to bend backwards at the extremities. These 
two flexures, however, from the nature and con- 
struction of the machine, must be very slight: and 
therefore a very small bend downwards and forwards 
given to the extremities of the axle, will be sufficient 
to counteract these effects, and render the lower 
surface of the arms of the axle nearly horizontal 
within the naves of the wheels. 
Great care should be taken not to give the axle at 
its entrance into the nave of the wheel too great.a 
bend, as is sometimes customary, particularly in Eng- 
land. The bad effects of this are, to cause the 
wheels to be formed somewhat of the shape of the 
frustrum of a’ cone, of which the vertex is at some 
distance from the carriage, nearly in the direction 
of the axle, whereby the wheel, instead of pro- 
ceeding forward, naturally has a tendency to move 
round the imaginary vertex of the cone just allud- 
ed to, as a centre, revolving obliquely, producing 
an irregular and unfavourable action of the parts 
in contact, and increasing friction. It is likely, in- 
deed, that the axle in the rude machines of early 
ages was at first straight, but as improvements were 
introduced, it would in time receive such modifica- 
tions as the judgment or caprice of the constructor 
might suggest. Still, however, there seems to be no 
just objection to the axle being nearly straight, in 
order to insure the best and easiest motion to the 
wheels, provided the part within the nave be truly 
cylindrical and of equal diameter throughout, though 
