MECHANICS. 69 i 
fhata fimilar invention might be applied to works of great 
utility ; it might be employed, for example, in the con- 
ftruftion of wheels to be always immerfed in water, their 
axis being placed parallel to the current : to give the wa¬ 
ter more activity, this helicoid wheel might be inclofed in 
a hollow cylinder, where the water, when it had once en¬ 
tered, being impelled by the current above it, would in 
our opinion aft with a great force. If the cylinder were 
placed in an ereft polition, fo as to receive a fall of water 
through the aperture at the top, the water would turn the 
wheel and its axis, and might thus drive the wheel of a 
mill, or of any other machine. Such is the principle of 
motion employed in the wheels of Baffacle, a famous mill 
at Touloufe. 
The fmoke-jacks in England are made fomewhat dif¬ 
ferent from that above delcribed ; being moftly after the 
manner of that exhibited in fig. 58. where AB is a circle 
containing the fmoke-vanes, of thin fheet-iron, all fixed 
in the centre, but fet obliquely at a proper angle of incli¬ 
nation, The other end of the fpindle has a pinion C, 
which turnsthe toothed wheel D, on the fpindle of which 
is fixed the vertical wheel E, over which pafl'es the chain 
E F which turns the fpit below. There are other forms 
of this uf'eful machine alfo made ; but all or moft of them 
having the fame kind of vanes in the circle AB, inftead 
of the fpiral form in fig. 57. The wheel A B fliould be 
placed in the narrow part of the chimney, where the po¬ 
tion of the fmoke is fwifteff, and where alfo the greateft 
part of it muft ftrike upon the fails. The force of this 
machine depends upon the draught of the chimney, and 
the ftrength of the fire. 
Jack is alfo the name of an inftrument in common ufe 
for raifmg heavy timber, or very great weights of any 
kind ; being a powerful combination of teeth and pinions, 
and the whole inclofed in a ftrong wooden ftock or frame, 
BCD, and moved by a winch or handle H P ; the outfide 
appearing as in fig. 59. In fig. 60. the wheel or rack- 
work is lhown, being the view of the infide when the 
ftock is removed. It is not, however, drawn in the juft 
proportions and dimenfions; for the rack EF muft be 
fuppofed at leaft four times as long, in proportion to the 
wheel Q, as the figure reprefents it; and the teeth, which 
will be then four times more in number, to have about 
three in the inch. Now, if the handle HP be feveninches 
long, the circumference of this radius will be forty-four 
inches, which is the diftance or fpace the power moves 
through in one revolution of the handle ; but, as the pi¬ 
nion of the handle has but four leaves, and the wheel Q 
fuppofe twenty teeth, or five times the number, therefore, 
to make one revolution of the wheel Q, it requires five 
turns of the handle, in which cafe it paffes through five 
times forty-four or 220 inches ; but, the wheel having a 
pinion R of three leaves, tliefe will raife the rack three 
teeth, or one inch, in the fame fpace. Hence, then, the 
handle or power moving 220 times as fait as the weight, 
will raife or balance a weight of 220 times its own energy. 
And, if this be the hand of a man who can fuftain fifty 
pounds weight, he will, by help of this jack, be able to 
raife, or fuftain, a weight or force of 11000 lb. or about 
five tons weight. This machine is fometimes open be¬ 
hind from the bottom almoft up to the wheel Q, to let the 
lower claw, which in that cafe is turned up as at B, draw 
up any weight. When the weight is drawn or pulhed 
fufficiently high, it is kept from going back by hanging 
the end of the hook S, fixed to a lfaple, over the curved 
part of the handle at h. 
The accidents that frequently happen, in ufing the 
jack for railing large weights, from the want of a con¬ 
trivance to prevent the machine running back if the 
weight by any means overcomes the power, had long been 
oblerved. To proteft the workmen in luch cafes, Mr. 
Mocock, of Southwark, produced a jack, with a click 
and ratchet, fo contrived as to prevent that danger; fbr 
which the Society of Arts voted him a bounty oi twenty 
guineas, lie leaving a model with the Society for the ufe 
of the public. This improved jack appears not to differ 
much, either in principle or conftruftion, from thofe in 
common ufe ; except that a pall, or click, and ratchet, are 
applied in fuch manner as to hold the machine fall, if the 
weight overbalances the power, and thereby prevent any 
accident the workmen may be fubjeft to, by the running 
down of the machine; by which the men are frequently 
expofed to danger, efpecially on-board fliips in engage¬ 
ments ; when, from inattention or negleft in fixing the 
hooks, or from any other caufe, the jacks in common ufe 
fail in the working. This inftrument is reprefented at 
fig. 61. A, A, the double handles of the winch. B, the 
large toothed wheel, in which the pinion on the axis C 
works. D, a ratchet-wheel. E, the click or pall, which, 
falling into the teeth of the ratchet, prevents the machine 
running back, if the weight fliould overcome the power. 
F, the rack, as in common jacks. We are of opinion that 
this improvement might ealily be applied to jacks already 
made; but we are not aware that it has been afted upon. 
Pile-Engines. Plate XVI. 
Piles are beams of timber, or flakes of wood, driven 
firmly into the ground, for various purpofes; as, for - 
forming a firft foundation for buildings, piers of bridges, 
&c. in which cafes they are driven quite down into the 
ground, or are cut off level with its lurface, with a view 
of obtaining a folid bearing for the weight of the ftrufture- 
which is to be railed. Amtlerdam, and fome other cities, 
are wholly built upon piles. The ftoppage of the breach 
in the banks of the Thames at Dagenham, was effefted 
by dove-tail piles ; that is, by piles mortifed into one 
another by a dove-tail joint. Piles are not employed for 
foundations unlefs the ground is fufpefted to be unfound, 
or when the weight to be borne is exceedingly great. 
They aft to make the foundation folid, by reaching deep 
into the earth, down to a more fubftantial ftratum than 
that of the furface. Indeed, the manner of fixing the 
piles, by driving them by repeated blows of a powerful 
machine till they will go no farther, enfures that they 
come to a good bearing. There are inftances of piles 
being driven down twenty-five feet, before they were 
thought fufficiently firm. 
Piles are alfo ufed for making the faces of wharfs, banks 
of rivers, piers for the fea, See. For thefe purpofes they 
are driven in rows, but only a fufficient depth in the earth 
to make them hand firm, and fupport the planking or 
framing which is fixed againft them. Thefe piles are 
ufually driven rather in an inclined pofition. For tempo¬ 
rary defence againft the water, in laying the foundation 
of bridges, &c. piles are always required. They are em¬ 
ployed in different ways to form an enclofure, or water¬ 
tight wall, called a coffer-dam, round the area where the 
work is to be laid, and from which fpace the water is 
drawn by pumps. This is the moft difficult of all kinds 
of piling; becaufe it muft Hand a great height above the 
ground, have fufficient ftrength to refift the preffure of 
water, and be perfectly clofe and tight. In navigable ri¬ 
vers detached piles are driven, and very firmly fixed, to 
mark the enclofures where barges are to lie, and to fender 
off others from them, as well as to moor them to. 
Piles are in general formed of a fquare timber, tapering 
if the tree happens to be fo, cut -5,0 a (harp point at one 
end, and fhod with iron to enter the ground. The other 
end is bound by a'Wrong iron hoop, to prevent the pile- 
liead fplitting by the violence of the blows which drive 
it down. 
Many different machines are ufed to drive piles into 
the ground ; fome of them are worked by a great number 
of men, who raife a heavy weight a fmall height, and let 
it fall upon the pile, till, by reiterated blows, they drive 
it to the required depth. The machine employed is ex¬ 
tremely fimple. A long thick plank of wood is fixed up 
clofe to the pile, having a mortife through the upper end, 
in which a pulley is fitted ; a rope goes over this to fuf* 
pend the rammer, which is a large block of hard wood,. 
properly 
