MECHANICS. 
creeled j but we have not feer» any account of its per¬ 
formance. It is a very intricate machine in its principles ; 
and ari ignorant engineer, nay the molt intelligent, may 
ereft one which fnall hardly dp any thing 5 and yet, by a 
very trifling change, may become very powerful. We 
prefume that failures of this kind have turned the atten¬ 
tion of engineers from it ; but we are perfuaded that it 
may be made very effective, and we are certain that it mull 
be very durable. Fig. 91. is a feftion of the manner in 
which the author has formed the communication between 
the fpiral and the rifing-pipe. P is the end of the hollow 
axis which is united with the folid iron axis. Adjoining 
to P, on the under f:de, is the entry from the la It turn of 
the fpiral. At Q is the collar which refts on the fupports, 
and turns round in a hole of bell metal, ff is a broad 
flanch call in one piece with the hollow part. Beyond 
this the pipe is turned fomewhat fmaller, very round and 
fmooth, fo as to fit into the mouth of the riling-pipe, like 
the key of a cock. This mouth has a plate ee attached 
to it. There is another plate dd, which is broader than ee, 
and is not fixed to the cylindrical part, but moves eafily 
round it. In this plate are four (crews, fuch as g, g, which 
go into holes in the plate ff, and thus draw the two 
plates ff and dd together, with the plate ee between them. 
Pieces of thin leather are put on each fide of ee-, and thus 
all efcape of water is effectually prevented, with a very 
moderate contpreffion and friction. 
Archimedes's Screw .—The fcrew-engine or fpiral-pump, 
called by the Germans the water-fnail, invented by Ar¬ 
chimedes, is reprefented. at fig. 93. where A B is a cylin¬ 
der, with a flexible-pipe, CEHOGF, wrapped round its 
circumference like a fcrew. The cylinder is inclined to 
the horizon, and fupported at one extremity.by the bent 
pillar IR, while its other extremity, furnilhed with a pi¬ 
vot, is immerfed in the water. When, by means of the 
handle K, the cylinder is made to revolve upon its axis, 
the water which enters the lower orifice of the flexible 
pipe is raifed to the top, and dilcharged at D. On fome 
occafions, when the water to be raifed moves with a con- 
fiderable velocity, the engine is put in motion by a num¬ 
ber of floatboards fixed at L, and impelled by the current; 
and, if the water is to be raifed to a great height, another 
cylinder is immerfed in the veflel D, which receives the 
water from the firll cylinder, and is driven by 3 pinion 
fixed at I. See the Frontifpiece. In this way, by having 
a fucceflion of fcrew-engines, and a fucceliion of reler- 
voirs, water may be railed to any altitude. An engine 
of this kind is defcribed in Fergufon’s Leisures, vol. ii. 
P- 113- 
In order to explain the reafon why the water rifes in the 
fpiral tube, let A B, fig. 94. be a fedtion of the engine, 
BCt/DE the fpiral tube, BF a horizontal line, or the 
furface of the flagnant water which is to be raifed, and 
ABF the angle which the axis of the cylinder makes with 
the horizon. Then, the water which enters the extremity 
B of the fpiral tube will defcend to C, and remain there 
as long as the cylinder is at relt. But, if a motion of ro¬ 
tation be communicated to the cylinder, fo that the lowed 
part C of the fpiral BCD move towards B, and the points 
d, D, E, towards C, and become fuccellively the lowed 
parts of the fpiral, the water mud occupy fucceflivelv the 
points d, D, E, and therefore rife in the tube ; or, which 
is the fame thing, when the point C moves toe, the point d 
will be at C ; and, as the water at C cannot rife along 
with the point C to C, on account of the inclination of Cc 
to the horizon, it mud occupy the point d of the fpiral, 
when C has moved to c; that is, the water has a tendency 
to occupy the lower parts of the fpiral, and the rotatory 
motion withdraws this part of the fpiral from the water, 
and caufes it toafeend to the top of the tube. By wrap¬ 
ping a cord round a cylinder, and inclining it to the ho¬ 
rizon, fothat the angle ABC may be greater than the an¬ 
gle ABF, and then making it revolve upon its axis, the 
preceding remarks will be clearly illudrated. If the di- 
Vol. XIV. No. 1011. 
761 
reflion of the fpiral BC (liould be horizontal, that is, if it 
fhould coincide with the line B F, the water will iiave no 
tendency to move towards C, and therefore cannot be 
raifed in the tube. For a fnnilar reafon, it will not rife 
when the point C is above the horizontal line BF. Con- 
fequently, in the conltruition of this engine, the angle 
ABC, which the fpiral forms with the fide of the cylinder, 
mud always be greater than the angle ABF, at which the 
cylinder is inclined to the horizon. In practice, the an¬ 
gle of inclination ABF lhould generally be about 50 0 , 
and the angle ABC about 63°. 
The theory of this engine is treated at great length by 
Hennert,in WisDiJfertationfur la Vis d' Archimede, Berlin,i 767 ; 
by Pitot, in the Memoirs of the French Academy, and by 
Euler in the Nov. Comm. Petrop. tom. v. An account of 
Pitot’s inveftigations may be fee 11 in Gregory’s Mechanics, 
vol. ii. p. 348. 
Bramah's Hydrojlalic Prefs. —This machine, invented by 
Mr. Bramah of Piccadilly, depends upon the principle, 
that any preffure exerted upon a fluid mafs is propagated 
equally in every direftion. It is reprefented at fig. 95. 
where A is a (frong metallic cylinder, furnilhed with a 
pilton B perfectly water-tight. Into the bottom of this 
cylinder is inferted the end of the bent tube C, the inte¬ 
rior orifice of which is doled by the valve D. The other 
extremity of the tube communicates with the forcing- 
pump E, by which water or other fluid may be driven into 
the cylinder A. Then, if any preffure is exerted on the 
furface of the water in the cylinder E by means of the 
lever H, this preffure will be propagated to the cylinder A, 
and exert a certain force upon the piflon B, varying with 
the relpeftive areas of the feftions of each cylinder. If 
the diameter of the cylinder E is equal to the diameter of 
the cylinder A, and if a force of 10 pounds is exerted at 
the handle H, then the piflon B will be elevated with a 
force of 10 pounds ; if the diameter of E be one-half that 
of A, the pilton B will be raifed with a force of 40 pounds, 
becaufe the area of the one piflon is four times the area of 
the other. Or, in general, if D be the diameter of the 
cylinder A, d that of the cylinder E, and F the force 
FxD 2 
exerted at the lever II, we (hall have d 2 : D 2 =nF : ———, 
d 2 
which is the force exerted upon the piflon B. Thus, if 
dzm inches, D=.2^. inches, and F:=io pounds, then 
-=-=1440 pounds, the force with winch 
d 2 2X1 
the piflon B is elevated. Now, as this force increafes as 
d 2 diminilhes, or as F and D 2 increafe, there is no limit 
to the power of the engine j for the diameter of the cy¬ 
linder A may be made of any lize, and that of the cylinder E 
exceedingly fmali, while the power may be (till farther in- 
creafed by lcngthening<jthe lever H. The fame effedts may 
be produced by injecting air into the pipe C by means of 
a large globe fixed at its extremity. Upon the lame prin¬ 
ciples the power and motion of one machine may be com¬ 
municated to another; for we have only to connedt the 
two machines by means of a pipe filled with water, inferted 
at each extremity into a cylinder furnilhed with a pilton. 
By this means the power which deprefles one of the piltons 
will be transferred along the connecting-pipe, and will 
elevate the other piflon. In the fame way water may be 
raifed out of wells of any depth, and at any diltance from 
the place where the power is applied. But we mult refer 
the reader, for a detailed account of thefe applications, to 
the fpecification of the patent obtained by Mr. Bramah ; or 
to Gregory’s Mechanics, vol. ii. p. 120. 
The Ptrfiav Wheel. —This is an engine which raifes water 
to a height equal to its diameter. C D E (fig. 96.) is the 
w heel, driven by the ftream A B, adling upon floatboards 
fixed on one fide of its rim. A number of buckets, a, a, a, a , 
are difpofed on theoppofite fide of the rim, and fufpended 
by Itrong pins, b, b, b, b, See. When the wheel is in mo¬ 
tion, the delcending buckets immerfe into the ftream, and 
9 H al'cens*. 
