1804, | 
linder, the top communicates with the 
condenfer. 
When the fingle-power engine is ufed, 
that is, when the fteam is made only to 
act againft the bottom of the pifton, and 
the top of the cylinders left open, two 
fteam cylinders are to be ufed inftead of 
one. The force of the engine may be 
rendered fo nearly equal in every part of 
its revolution, as to a&t with a much 
fmaller fly than is commonly made ufe of ; 
but inthis cafe, the pifton of the cylinders 
are made to a& on two arms of one crank, 
placed at right angles to each other; and 
the valve is not to vibrate, but to revolve 
on its axis, making one turn to each ftroke 
of the engine. 
Mr. Freemantle next defcribes the prin- 
ciple on which his parallel motion de- 
pends, and the method of conftruéting it; 
here he is obliged to have recourfe toa 
mathematical problem, the folution of 
which requires the aid of figures. 
Another improvement is in the cold 
water pump, which will obviate the in- 
conveniences arifing from the inner lid of 
the afcending columns of water, and alfo 
prove of confiderable utility when the 
pipes leading to the pump-barrel are too 
fmall, or when the motion of the pifton 
in the barrel is very quick. This im- 
provement confifts in placing an air veffel 
fo as to communicate with the afceading 
column of water immediately below the 
lower valve of the pump. Now it is evi- 
dent, that before water can be raifed into 
the barrel, a partial vacuum will be made 
in the air veflel, and the rarity of the air 
in it will be proportional to the heizht of 
the veflel above the furface of the water 
in the weil, fince the water can afcend in 
the barrel only with a determinate velo- 
city, and which depends on the height of 
the pifion above the furface of the water 
jn the well, and alfo on the diameter of 
the pipe. It fometimes happens, that the 
velocity of the pifton exceeds that of the 
water, and a vacuum is formed between 
the bottom of the pifton and the furface 
of the column of water ; hence a violent 
concuffion is produced, which is detri- 
mental to the pump and any apparatus 
connected with it; the air veffel will pre- 
vent thofe difagreeable effects from taking 
place, for, inftead of a vacuum being 
formed below the pifton, air wiil be ex- 
tracted from the air veffel; and, as the 
pilton defcends, the preflure of the air on 
the furface of the water in the well not 
being counterbalanced, will continue to 
sife into che veffel till the equilibrium is 
reftored; and when the piiton afcends 
New Patents lately enralled, 
51 
again, the barrel will not only be fupplied 
by the pipe, but alfo by the water in the 
air veffel, fo that the pifton muft require 
lefs force to lift than if there were no air- 
veffel. 
Such are the leading obje&s which this 
patent embraces ; and we are affured that 
a fteam-engine, conftructed on thefe prin- 
ciples, has been erected at Bedworth, near 
Coventry, which an(wers exceedingly well, 
MR. CATHCART DEMPSTER'S (ST. AN- 
DREW’S) fu IMPROVEMENTS in the 
MANUFACTURE Of CANVASS, &e. for 
SAILS, TENTS, PACKAGES, aad other 
ufeful PURPOSES. 
By the common method, fingle yarns, 
not twilted, but glued together with 
ftarch or other mucilage, are ufed in form- 
ing the warp of the canvas, which renders 
it liable to deftruction by miidew. Mr, 
Dempfter makes ufe of twine, compoled 
of two or more yarns of prime material, 
of equal fize and ftreneth, both for 
warp and woof. By this means, he 
weaves his canvafs without ftarch, or any 
other mucilage, and is able to produce au 
article nearly twice as {trong as common 
canva{s of the fame weight and finerefs, 
and with this advantage, that its threads 
have an equal bearing on one another in 
all direétions, not liable, like the common 
canvats, to fplit longitudinally, being 
much ftronger in the crofs direction, not 
liable to the mildew, aud extremely dura- 
ble, becaufe it is {ubject to-no irregular 
action of fharp cutting threads on its 
woof, but is only expofed to the fair, flow, 
and gradual wear of its weil combined 
and duly proportioned component parts, 
which maintain their relative ftrength to 
the laft. 
ne 
tne 
MR. JOHN CANT’S and MR. JOHN MIL~ 
LAR’S (MONTROSE) jor a new ME- 
THOD 0f TANNING LEATHER. 
The method made ufe of by thefe gen- 
tlemen for preparing hides and ikins by 
liming, hairing, flefhing, and but .g, is 
the fame as that made ule o! by 
experienced tanners, excepting that in 
raifing the hides intended for butts and 
backs, they prefer acids made of rye ra- 
ther than of vitriol 
According to their invention, they erect 
a boiler of copper, or any other imeial tho: 
does not ftain the tan or liquor, wh: 
they fill half full of grouna bark 
having filled. it up with-wate:, cicy 
it about three hours, till the tanyi 
ciple is completely extagiec. Tike 
2 
sa ww 
LHe Morr 
