r»to 
MECHANICS. 
belongs to it. This arm was permitted to move up and 
down by means of a hinge, fo as to let the wheel rife over 
any obliacle which was placed in its way. Befides this, 
another arm, M, was placed above that which carried the 
wheel, at the extremity of which was fattened a piece of 
tin, N, forming a vane, which, by its refiftance to the air, 
regulated the motion of the machine. The roller was now 
made to turn, by putting weights into the fcale, and it 
was let to revolve until its motion became uniform. Af¬ 
ter eight or ten turns it revolved with an equable velocity, 
and during every fet of experiments the fame velocity was 
preferved ; and whatever refiftance the carriage was ex- 
pofed to was overcome by the addition of weight. The 
additional weight became therefore, in all cafes, the mea- 
fure of the additional refiftance, and determined, with 
the greateft accuracy, the refult of every experiment I 
wiftied to try. 
Having found that nearly five pounds and a half was 
fufficient to give the wheel, W'hen loaded fo as to weigh 
about four pounds, a velocity of nearly ten feet in a fe- 
cond, I placed an obftacle of a quarter of an inch high 
upon the plane, and it required no lefs than fix pounds 
and a half to overcome its refiftance. Two fuch obftacles 
required fourteen pounds and a half. Two obftacles of 
the fame height, but of a different (hape, each making an 
inclined plane of three quarters of an inch long, and a 
quarter of an inch high, were fubftituted in the place of 
the former, and it required but two pounds to overcome 
their refiftance. The difference, therefore, between two 
and fourteen muft be attributed to vis inertia ; for, the ve¬ 
locities of the carriage and the heights of the obftacles re¬ 
maining the fame, the only difference that exifts is, that 
in the one cafe the wheel has much more time to furmount 
the obftacle than in the other, and confequently has much 
lefs vis inertia to overcome. 
From this confideration it appears, that whatever per¬ 
mits the load to rife gradually over an obftacle, without 
obftrudting the velocity of the carriage, will tend to faci¬ 
litate its draught; and the application of fprings has this 
effect to a very confiderable degree ; the fame weight of 
four pounds being drawn over the fame obftacles, when 
fprings were put between the load and the carriage, by- 
four pounds inftead of fourteen. This remarkable dif¬ 
ference points out the great advantage of fprings in rough 
roads ; an advantage which might be obtained for heavy 
waggons, as well as for other carriages, by a judicious ap¬ 
plication of the fame means. 
It has but feldom happened that the modefty of theory 
has promifed lefs than what has been verified by experi¬ 
ment ; but it appears, from the Memoirs of the French 
Academy, that the idea of applying fprings to carriages 
had occurred to M. Thomas in the year 1703, who has 
given a drawing of a carriage, conltruCfed upon this prin¬ 
ciple, many years before it was attempted to be put into 
execution. So little hopes had he entertained of fuccefs, 
that he exprefsly mentions it as a theory which could not 
be reduced to practice; he had, however, no notion of 
applying fprings to facilitate the draught, but merely for 
the convenience of the rider; and I apprehend that it is 
not at prefent commonly imagined that fprings are advan¬ 
tageous for this purpofe, nor would it at firlt fight appear 
credible, that upon a rough paved road, fuch as is common 
in Cheftiire, and other parts of England, a pair of horfes 
could draw a carriage mounted upon fprings with greater 
eafe and expedition than four could draw the fame car¬ 
riage if the fprings and braces were removed, and the 
carriage bolted fait down to the perch. I tried fome other 
experiments, with the fame apparatus, to compare long 
and lhort, high and low, carriages. I have loft the parti¬ 
cular refults of each experiment; but I am well affured 
that the preference, which has lately been given in Eng¬ 
land to high carriages, is ill-founded ; that, upon fmooth 
roads, the height of the carriage is a matter of indiffer¬ 
ence as to the draught, and that in rough roads it is con- 
fiderably difadvantageous; that the length of carriages, 
if their weight be not increafed, is alfo a matter of indiffer¬ 
ence, except in very uneven roads, and where there are 
deep ruts; in the former, long carriages are preferable; 
in the latter, lhort ones, 
I fubjoin a Table of the Experiments; from which the 
mechanic may draw many ufeful obfervations, and which 
may fupply the mathematician with many curious and 
elegant fubjects of inveftigation. It Ihould be premjfed^ 
that the weight of the load was 31b. the weight of the load, 
wheel, carriage, &c. 4.1b. the fcale and weight defcended 
fix inches and two-tenths every revolution of the roller; 
the diameter of the wheel was two inches nine-tenths; and 
the circumference of the circle upon which the wheel ran 
was ten feet three inches and a quarter. 
Experiments. 
1. A vane of tin, 11 inches long and 5J broad, 
fattened to an arm projedting from the rol¬ 
ler, to regulate the motion of the machine 
by its refiftance againft the air 5 the extre¬ 
mity of the vane 21 inches from the centre 
of the roller, made - 
2. The fame as N°i. with the wheel running 
upon the iron circle - 
3. The fame as N° 2. but with an obftacle of 
£ inch high, placed on the road 
4. The fame as N° 2. but with two obftacles 
5. Do. with two inclined planes, \ inch high, 
l inch long, inftead of the obftacles 
6. Springs placed between the weight and the 
wheel, two obftacles £ inch high, placed on 
the road - - 
7. Same as N° 1. with half the velocity 
2 . Same as N° 4. with half the velocity 
9. Same as N° 6 . with half the velocity 
Turns 
20 
20 
20 
20 
20 
20 
10 
10 
Time Weights. 
Seconds 
20 
20 
20 
20 
20 
20 
20 
20 
lb. oz. 
10 
12 
20 
Observations. 
1. The refiftance of the air againft the vane, 
and againft all the moving parts of the ma¬ 
chine, was equal to 
This weight muft therefore be deducted from 
the weights ufed in the fubfequent expe¬ 
riments 
4 lb. 10 oz. being deducted for the refift¬ 
ance of the air from 5 lb. 10 oz. the re¬ 
mainder was the refiftance occafioned by 
the motion of the wheel on the fmooth board 
3. The refiftance of an obftacle of £ inch high 
4. The refiftance of two obftacles of £ inch high 
The refiftance of inclined planes, inftead 
of abrupt obftacles - 
6. The refiftance of two obftacles £ inch 
high, when fprings were ufed, only 
7. Refiftanceoftheairtohalftheformervelocity 
8. Refiftance of two obftacles, with half the, 
former velocity - 
9. Refiftance of ditto with fprings - 
lb. oz. 
4 i® 
1 o 
6 6 
14 6 
1 14 
3 
1 6 
6 * 
z % 
Of fome late Improvements in Wheel-Carriages. 
In the year 1814, Meffrs. Barclay and Cuming, of Cam¬ 
bridge, coach-makers, obtained a patent for the conftruc- 
tion of improved wheels and axle-trees,of fuperior ftrengtli, 
durability, and fafety, to thofe in common ufe. 
Fig. 5. reprefents a bird’s-eye view of the nave of the 
wheel, made ofcaft-iron, brafs, bell-metal, or any fuitable 
material, the mortices therein being made wider at the bot¬ 
tom thai? the top, fo as to allow the tenon of the fpoke to 
expand Vlien driven into effeft ; and there is previoufly 
made 
5 
