802 
of making the middle or‘shank of the 
fore-axle in the form of an arch, in 
order to combine a high fore-carriage 
with a low fore-wheel, to support the 
fore-transom and fore.end of the perch 
on alevel with the hind transom and the 
hinder end of the perch; but as the 
fore axle'thus arched is out of line, the 
arms of it are thereby deprived of a 
part of their power to resist shocks from 
stones and other obstacles in. the road, 
and are proportionably subject to a 
drag or heaviness.in draft. , A frequent 
cause of heaviness in draft is the use of 
very short perches, so prevalent in stage 
coaches, from. an erroneous opinion, 
that, because the tardy movement of 
the hind wheels is less evident to the 
the coachman with a short perch, that 
therefore such a. carriage “ follows 
well,” in the coachman’s phrase; but it 
is obvious that the end-of a short perch 
must be raised to a higher angle from 
the road than the end of a long perch, 
to enable either the fore or hind wheels 
to get over a stone or other obstacle, 
and requires a greater power so to raise 
the end. of a short perch, and with it 
one-half the weight of the carriage, which 
is equivalent to heaviness in draft; the 
perch should be fully as long as is re- 
quired by the use and superstructure of 
the carriage, there being no limit to the 
length of the perch but that of super- 
fluous weight, or the excess of the arch 
that must be described by one or both 
ends of the perch in turning the car- 
riage. Heaviness in draft is also fre- 
quently caused. by the use of modern 
elliptic and grasshopper springs, espe- 
cially the former, between the axles and 
the axle beds, because those springs se- 
parate the centres of the wheels so far 
from the axle beds and main frame of 
the carriage, that. the power of the 
wheels to resist shocks is lessened, and 
the springs are subject. to a drag, which 
is very. distressing to horses in soft or 
deep-roads; though it eludes observation 
upon pavement, where’ such a carriage. 
appears to run light ; besides which, the 
use of such springs has. occasioned the 
size of the fore wheels, which were be- 
fore too small, to be further reduced of 
late years, in order to gain room for the 
play of these springs, but to the great 
distress of the -horses. And, lastly, hea- 
viness in; draft is caused by the too fre- 
quent use, of iron in modern carriages, 
in order to indulge. fancy of design ; but 
much of that heavy and non-elastic ma- 
terial might be dispensed with, if coach- 
makers would prefer iron clamps. to 
On the Construction of Four-Wheel Carriages. 
(Nov. I, 
screw bolts,-as less wood and iron 
would then have as much strength, 
Having’ shewn that the chief de- 
fects of common carriages originate 
from the centre of action being in a 
wrong place, viz. at the perch-bolt of 
the fore-carriage, and from the want of 
lateral or spinning action in the.hind 
wheels, it remains to be shewn that 
the centre of action ought to be half 
way between the two axles at or under 
the centre of gravity, and that the fore 
and hind wheels, or the two axles on 
which they turn, should have an alter- 
nate equal and simultaneous action. 
Now as the power of a carriage to turn 
more or less suddenly, or in a greater 
or lesser space, is in proportion to the 
inclination of the axis of each pair of 
wheels to the axis of the other pair, if 
one or two axles be turned obliquely ; 
it follows, that by dividing the above- 
mentioned obliquity of the fore axle of 
common carriages, which is equal to an 
angle of 45°, or but little more, between 
the fore and hind axles, through the 
means of an alternate equal and simul- 
taneous action to be giveu to both 
axles, it would be unnecessary for the 
fore axle to turn more than to an angle 
of 2229, or yery little more, which obli- 
quity would admit of the fore wheels 
being as large as the hind wheels. 
Professor Gregory has recommended 
wheels of equal sizes as a most desir- 
able property, but-he has not given any 
hint or hope that it could be attained 
by any method applicable to carriages 
for travelling and recreation; and here 
it should be obseryed, that some gentle- 
men of practical authority, who were 
examined before a Committee of the 
House, of Commons upon this subject, 
concurred in stating, that wheels of four 
feet. six inches diameter are the most 
eligible, which size is perfectly adapted 
to all the wheels of a carriage with the 
proposed alternate action, The writer 
conceives, however, that wheels four 
feet four inches diameter, are large 
enough for ease in draft, and for ele- 
gance, - ' 
To illustrate the mathematical pro- 
priety of placing the centre. cf action at 
or under the centre of gravity, by giv- 
ing an alternate equal and simultaneous 
action to the two axles, or two pair of 
wheels. Let us suppose a carriage 
made on a principle directly the con- 
trary of that which is in common use, 
viz. with the fore axle fixed, and the 
hind axle to turn on a perch-bolt like a 
common fore axle: it will be found that 
such 
