i <-* 
M E C H A N I C S. 
lation, it occurred to MY. Newcomen that the vacuum he 
to much wanted might be produced by (team, and that 
this gave rife to his new principle and con It ruction of the 
fteam-engine. The Specific defideratum was in Newco¬ 
men’s mind ; and therefore, when Savery’s engine ap¬ 
peared, and became known in his neighbourhood many 
years after, he would readily catch at the help which it 
promiled. Savery, however, claims the invention as his 
own ; but Switzer, who was perfonally acquainted with 
both, is pofitive that Newcomen was the inventor. By 
his principles (asaquaker) being averfe from contention, 
he was contented to Share the honour and the profits with 
Savery, whofe acquaintance at court enabled him to pro¬ 
cure the patent in 1705, in which all the three were affo- 
ciated. Pofterity has done juftice to the modeft inventor, 
and the machine is univerfally called Newcomen’s Engine. 
Its principle and mode of operation may be clearly con¬ 
ceived as follows : 
Let A (fig. 113.) reprefent a great boiler, properly built 
in a furnace. At a fmall height above it is a cylinder 
CBBC of metal, bored very truly and fmoothly. The 
boiler communicates with this cylinder by means of the 
throat, or fteam-pipe, N Q. The lower aperture of this 
pipe is (hut by the plate N, which is ground very flat, fo 
as to apply very accurately to the whole circumference of 
the orifice. This plate is called the regulator, or fleam* 
cock 5 and it turns horizontally round an axis b a, which 
pafles through the top of the boiler, and is nicely fitted 
to the focket, like the key of a cock, by grinding. The 
upper end of this axis is furniflied with a handle £T. A 
pifton P is lufpended in this cylinder, and made air-tight 
by a packing of leather or foft rope, well filled with tal¬ 
low ; and, for greater fecurity, a (mail quantity of water 
is kept above the pilton. Thepiflon-rod P D is fuipended 
by a chain which is fixed to the upper extremity F of the 
arched head F D of the great lever or working-beam H K, 
which turns on the gudgeon O. There is a fimilar arched 
head E G at the otiier end of the beam. To its upper 
extremity E is fixed a chain carrying the pump-rod X L, 
■which raifes the water from the mine. The load on this 
end of the beam is made to exceed confiderably the weight 
of the pifton P at the other extremity. At fome fmall 
height above the top of the cylinder is a ciftern W, called 
the injettion cijfern. From this defcends the injeftion-pipe 
ZSR, which enters the cylinder through its bottom, and 
terminates in a fmall hole R, or fometimes in a nozzle 
pierced with many fmaller holes diverging from a centre 
in all directions. This pipe has at S a cock called the 
injeSion cock, fitted with a handle V. At the oppofite fide 
of the cylinder, a little above its bottom, there is a late¬ 
ral pipe, turning upwards at the extremity, and there co¬ 
vered by a clack-valve f, called the fnifting valve, which 
has a little difh round it to hold water for keeping it air¬ 
tight. There proceeds alfo from the bottom of the cy¬ 
linder a pipe degh (palling behind the boiler), of which 
the lower end is turned upwards, and is covered with a 
valve h. This part is immerfed in a ciftern of water Y, 
called the hot well, and the pipe itfelf is called the educ- 
iion-pipe. Laftly, the boiler is furnifned with a fafety-valve 
called the puppet-clack (which is not represented in this 
Sketch for want of room), in the fame manner as Savery’s 
engine. This valve is generally loaded with one or two 
pounds on the fquare inch, fo that it allows the fleam to 
efcape when its elafiicity is one-tenth greater than that 
of common air. Thus all rifk of burlting the boiler is 
avoided, and the preirure outwards is very moderate; fo 
alfo is- the heat. 
Thefe are all the efiential parts of the engine. Let us 
now fee how it is put in motion, and what is the na¬ 
ture of its work. The water in the boiler being fuppofed 
to be in a ftate of ftrong ebullition, and the fleam iffuing 
by the fafety-valve, let us confider the machine in a ftate 
of reft, having both the fteam-cock and injeftion-cock 
Shut. The refting polition or attitude of the machine 
inuft be fuch as appears in Iketch, the pump-rods prepon- 
Vox.. XIV. No. ioiz, 
derating, and the great pifton being drawn up to the top 
of the cylinder. Now open the fteam-cock by turning 
the handle T of the regulator. The fteam from the boiler 
will immediately rufh in, and, flying all over the cylin¬ 
der, will mix with the air. Much of it will be condenled 
by the cold Surface of the cylinder and pifton; and the 
water produced from it will trickle down the tides, and 
run off by the edu£tion-pipe. This condensation and 
wal'te of fteam will continue till the whole cylinder and 
pifton are made as hot as boiling water. When this hap¬ 
pens, the fteam will begin to open the fnifting-valve j, 
and. iffne through the pipe ; llowly at firft and very cloudy, 
being mixed with much air. The blaft at f will grow 
Stronger by degrees, and more transparent, having already 
carried off' the greateft part of the common air which 
filled the cylinder. We fuppofed that the water was 
boiling brifkly, fo that the fteam was iffuing by the fafety- 
valve which is in the top of the boiler, and through ever-y 
crevice. The opening of the fteam-cock puts an end to 
this at once, and it has fometimes happened that the 
cold cylinder abstracts the lteam from the boiler with 
fuch aftonilhing rapidity, that the preffure of the atmo- 
fphere has burft up the bottom of the boiler. 
When the manager of the engine perceives that not 
only the blaft at the fnifting-valve is ftrong and Heady, 
but that the boiler is now fully fupplied with fteam of a' 
proper ftrength, appearing by the renewal of the difcbarge 
at the fafety-valve, he Shuts the fteam-cock, and opens 
the inje£tion-cock S by turning its handle V The pref¬ 
fure of the column of water in the injedtion-pipe ZS im¬ 
mediately forces fome water through the fpout R. This, 
coming in contaft with the pure vapour which now fills 
the cylinder, condenfes it, and thus makes a partial void, 
into which the more diftant fteam immediately expands, 
and by expanding collapfes, as has been already observed. 
Wiiat remains in the cylinder no longer balances the at- 
mofpherical preffure on the furface of the water in the 
injedtion-ciftern, and therefore the water fpouts rapidly 
through the hole R by the joint action of the column Z S 
and the unbalanced preffure of the atmofphere; at the 
fame time the fnifting-valve f, and the edudtion-valve h, 
are Shut by the unbalanced , preffure of the atmofphere. 
The velocity of the injedtion-water muff therefore rapidly 
increafe, and the jet will dafli (if Angle) againft the bot¬ 
tom of the pifton, and be Scattered through the whole 
capacity of the cylinder. In a very fhort lpace of time, 
therefore, the condenfation of the fteam becomes univer- 
fal, and the elafticity of what remains is almoft,nothing. 
The whole preffure of the atmofphere is exerted in the 
upper furface of the pifton, while there is hardly any on 
its under fide. Therefore, if the load on the outer end E 
of the working-beam is inferior to this preffure, it mult 
yield to it. The pifton P mult delcend, and the pump- 
pifton L mult afcend, bringing along with it the water 
of the mine ; and the motion mult continue till the great 
pifton reaches the bottom of the cylinder; for it is not 
like the motion which would take place in a cylinder of 
air rarefied to the fame degree. In this lalt cafe, the im¬ 
pelling force would be continually diminilhed, becaule 
the capacity of the cylinder is diminilhed by the defcent 
of the pilton, and the air in it is continually becoming 
more denfe and elaftic. The pifton would ftop at a cer¬ 
tain height, where the elalticity of the included air, to¬ 
gether with the load at E, would balance the atmofphe- 
rical preffure on the pilton. But, when the contents of 
the cylinder are pure vapour, and the continued ftream 
of injected cold water keeps down its temperature to the 
fame pitch as at the beginning, the elalticity of the re¬ 
maining fteam can never increafe by the defcent of the 
pifton, nor exceed what corresponds to this temperature. 
The impelling or accelerating force therefore remains the 
fame, and the defcent of the pifton will be uniformly ac¬ 
celerated, if there is not an increafe of refiffcance ariling 
from the nature of-the work performed by the other end 
of the beam. If the cylinder has been completely purged 
v 9 L of 
