1824..] 
such a carriage (by dividing the action 
between the fore and hind wheels, when 
turning, in a manner which is directly 
the reverse of the inovement of a com- 
mon carriage stated in the above excep- 
tion), will go direct to a turn, and keep 
the line of draft in turning, without re- 
quiring the preparatory movement which 
a common carriage is obliged to make to 
clear an obstacle; and that it will per- 
form this with a peculiar action, which 
is the opposite extreme, and greatly su- 
perior to that of a common carriage, 
because the hind wheels will move ra- 
pidly into the new line of draft through 
an arch of a circle, of which the perch 
is the radius. But as the moveable hind 
wheels of such a carriage must be not 
only smaller than the fore wheels, but 
smaller in a greater proportion, and 
with a greater power of turning than the 
fore wheels of common carriages, such 
a carriage would be subject to very un- 
equal motions at its extremities, which 
would render it unfit for rapid travel- 
ling and uneasy to passengers, though 
it is not liable to overset in turning on 
a descent like a common carriage, be- 
cause its fore-wheel would not withdraw 
its support. Hence appears the expe- 
diency of adopting a principle of action 
which is a medium between those two 
extremes, by placing the centre of action 
at or under the centre of gravity, and 
dividing the action between the two 
axles, or between the two pair of wheels, 
as either method would combine the 
good properties of the common action 
with those of a superior principle. 
The effect of dividing the angle requi- 
site for turning between the two axles, 
in reducing the obliquity of each axle to 
one-half the present obliquity of the 
fore axle of a common carriage, has 
been overlooked by Edgeworth in his 
work upon wheel carriages : he says that 
a carriage with an alternate action, pro- 
duced by intersecting chains, would not 
haye sufficient base or stability when 
turned; but he forgot that‘it is not ne- 
cessary for the axles of either of them 
to turn near so obliquely as the fore 
axle of a common earriage, and that 
though the circumferences of the con- 
verging wheels, if large, may approach 
near to the perch, the axles and wheels 
would still giye support to the carriage 
in precisely the same degree as’ the 
average of the support given by the two 
axles and the wheels of a common car- 
riage, with this great improvement, that 
in turning ‘the fore’ axle and wheels 
would give one-half more support. than 
, 
On the Construction of Four-Wheel Carriages. 
303 
they now do in a common carriage, and 
that the obliquity of the hind axle and 
wheels would place them directly in 
opposition to the tendency that ‘a com- 
mon carriage then has to upset, and 
would enable the hind wheels to obey 
the impulse they would receive by con- 
forming to the new line of draft without 
scraping the ground, so as to give uni= 
form support, which the hind wheels of 
a common carriage, at that very time 
when support is most wanted, in conse- 
quence of the excessive obliquity of the 
fore-axle and the impetus of the car- 
riage, not only fail to give, but even 
tend to destroy the small support that 
then remains. Besides which securities 
against upsetting, a carriage with an 
alternate action would turn the corners 
of streets, or in a cirele but little more 
in diameter than the length of the car- 
riage, without any preparatory move- 
ment at all deviating from the line of 
draft. 
It being possible that Edgeworth’s re- 
mark might have alluded to the invention 
by which Stewart, about fifty years ago 
produced an alternate action, by means 
of an endless and intersecting chain 
moved by horizontal wheels fixed on the 
perch bolts, and turning with their re- 
spective axles, it is right to mention, 
that although Stewart’s method does 
not exhibit, upon a trial by a model, 
any palpable loss. of tension in. the 
chains, yet it is obvious that a chain, 
or any loose or flexible substance, sus- 
pended between widely separated give 
and take wheels, and subject to a great 
strain and violent action, will not long 
preserve its tension, and that a chain in 
particular will, from the number of its 
links, become intolerably noisy to pas- 
sengers: besides, a chain, or any flexible 
substance, cannot have more than half 
the power that it ought to have, because 
such a material: has’ only the power. of 
pulling and not of pushing the alternate 
axles, and the impulse being given by 
the horses to the fore axle, it cannot 
re-act from the hind'axle: hence it ap- 
pears that Stewart’s method had not 
sufficient power; and’ it is remarkable 
that he’ made his fore wheels smaller 
than his hind’ wheels, but whether in 
conformity to custom, or from any sup- 
posed necessity, it is ‘difficult ‘to deter- 
mine, as he must have been too intelli- 
gent to be blinded by the former, or not 
to-perceive that there is no’ such neces- 
sity for small fore wheels with an alter- 
nate action. 
The necessity of endeavouring to re- 
medy, 
