MECHANICS. 
692 
and runs up to the pole, having a joint at f. This bar is 
neceftary to relieve the point ot the upright fpindle of the 
refinance oppofed to the wheels in moving along. The 
cutter can be placed higher or lower on the fpindle, fo as 
to cut the draw to any height, by means of a feries of 
holes through the fpindle ; pins palling through holes in 
the fockets of the arms, and the molt fuitable of the fe¬ 
ries. The cutter can alfo be fcrewed to any height from 
the ground; from two to eighteen inches, by means of an 
iron lever, g, on the point of which is-a brafs focket, in 
which the upright fpindle runs, and on which it relts by 
means of a ruffat h. The lever is hung by an iron chain, 
i, palling over a pulley at j, and joining two iron rods at 
k, which connect it with a fcrew box, l, whicti is moved 
backwards and forwards, by turning round the fcrew m. 
To the end of this fcrew is connected an iron rod, which 
runs along the upper fide of the pole to a bearing at n. 
At the end of this rod is a winch, 0, of nine inches radius, 
by which the perfon who guides the machine can turn 
round the ft < :w, and fo raife or lower the cutter at plea- 
fure. This is principally of ufe to raife the cutter when 
palling over a deep furrow, or in going from one field to 
another; p, is a hollow piece of wood put upon the end 
of the rod, by which the man holds with one hand when 
guiding the machine. In molt cafes, the cutters will cut 
a quarter of an acre without requiring to be fharpened, 
which can be done in two minutes by a i common Icythe- 
ftone, two of which are conveniently carried in two lea¬ 
ther pockets, q, fig. 40. When it is neceffary to go with 
the machine to a diltance, the upright fpindle, with the 
drum and cutter, are taken from their place, and placed 
on the top of the carriage ; and the fmall wheels are drawn 
clofe up to the crofs bar. The draught bar, D, is taken 
from the end of the pole, and placed near the frame of the 
carriage in the mortice, r, fig. 39. The horfes are turned 
•to draw from it, and can in this way travel any diltance, 
and over any roads. 
At a meeting of the Highland Agricultural Society of 
Scotland, fo recently as Jan. 13, 1816, a piece of plate of 
fifty guineas value, with a fuitable infcription, was voted 
to Mr. Smith, as a mark of the Society’s fenfe of the be¬ 
nefit rendered by him to agriculture, in conftrudiing an 
efficient machine for reaping grain, as certified fo refpedt- 
ably to the Society ; which the meeting would have been 
happy to have augmented, had the ftateand appropriation 
of the Society’s funds admitted of it; a hope was at the 
fame time expreffed, that Mr. Smith’s perfeverance and 
fuccefsful exertions would be more amply rewarded by 
the introduction of his machine into general ufe. The 
Society, at the fame time, confirmed the refolutior. of the 
directors to award a fum of 20I. to Mr. Kerr, on account 
of his model of a reaping-machine ; and empowered the 
directors to apply a farther fum of 20I. towards defray¬ 
ing the expeni’e of conftrudting an operating machine, 
upon the principles of that model, with fuch improve¬ 
ments as he may be able to make. 
Prony’s Condenser of Forces. 
This name was given by Mr. R. Prony to a contrivance 
for obtaining the greateft polfible effedt from a firlt mover, 
the energy of which is fubjedt to augmentation or dimi¬ 
nution within certain limits; and in general to vary at 
pleafure the reliltance to which the effort of the firft mover 
forms an equilibrium in any machine whatever, without 
changing any part of their conftrudtion. (Bulletin of the 
Philomathic Society at Paris, N° 83.) 
The general problem in mechanics, of which this con- 
denfer is intended as a practical folution, is enunciated 
by Mr. Prony in the following terms : “ Any machine 
being conftrudted, to find, without making any change in 
the conftrudtion, a means of tranfmitting to it the adtion 
of the firft mover, by fulfilling the following conditions, 
viz. 1. That it may be poffible at pleafure, and with great 
fpeed and facility, to vary the refiftance (againft which 
the effort of the firft mover mult continually make an 
equilibrium) in limits of Arty required extent. 2. That 
the refiftance, being once regulated, (hall be rigoroufiy 
conftant until the moment when it is thought proper to 
increale or diminifh the fame. 3. That, in the molt hid¬ 
den variations of which the effort of the firft mover may 
be capable, the variation in velocity of the machine fhall 
never undergo a folution of continuity.” 
Mr. Prony applies this folution of this problem to the 
dynamic effedt of wind ; but it will be eafy to make the 
fame general, when other firft movers are ufed. Fig. 45, 46, 
Plate XIII. reprefent the plan, and fig. 47 the eleva¬ 
tion, of the machine, the fame letters denoting the fame 
parts in each. Let O O be fuppofed the vertical axis 
of a windmill; eeee is an affemblage of carpentry, of 
which one of the radii, O e, bears a curved piece, bd, of 
iron or fteel : vertical axes of rotation a a a, being placed 
round the axis O O, they alfo divide the circumference 
in which they are found, into equal parts. Each of thefe 
axes carries a curve af, of iron, fteel, or copper ; fo fitu- 
ated, that, when the wind adts upon the fails, the curve 
bd preffes againft one of the curves aj\ and caufes the 
vertical axis to which this laft curve is affixed, to make a 
portion of a revolution. The curves bd and af mult 
be fo difpofed, that, when bd ceafes to prefs on one of 
the curves af, it fhall at the fame inftant begin to a 61 
upon the following curve : the number of axes which are 
provided with thefe curves, i^uft be determined by the 
particular circumftances of each cafe; and it is alfo prac¬ 
ticable to fubftitute, inftead of bd , a portion of a toothed 
wheel having its centre in the axis O O, and to place por¬ 
tions of pinions inftead of the curves af\ but the difpo- 
fitions reprefented in the figure are preferable. Each of 
the axes aaaa (which are all fitted up alike, though, for 
the fake of clearnefs, only one of them has its apparatus 
reprefented in the drawing) carries upon it a drum or 
pulley, ttrr, fig. 46. on which is wound a cord, p, that 
paffes over a pulley P, and ferves to fupport a weight Q, 
by means of the lever F G, upon which this weight may 
be Aided and faftened at different diftances from the 
point of motion G. The fame axes, a, a, pafs through 
the pinions q, q, fig. 47. to which they are not fixed ; but 
thefe pinions carry clicks or ratchets, which bear againft 
rr; fo that, when the weight Q tends to rife, the ratchet 
gives way, and no other effedt is produced on the pinion 
q q, either by the motion of the axis or of the drum ttrr , 
excepting that which caufes the afcent of the weight Q. 
But the inftant that the curve, or tooth, bd, ceafes to bear 
againft one of the curves af, after having caufed the cor- 
refponding weight Q to rile, that weight Q tends to re- 
defcend, and then the toothed wheel rr adts againft the 
ratchet, fo that Q cannot defcend without turning the 
pinion qq along with the drum ttrr. The pinion qq takes 
in the wheel A B, from the motion of which the ufeful 
effedt of the machine immediately refults; fo that the ef- 
fedt of the defcent of one of the weights Q is to folicit 
the wheel A B to motion, or to continue the motion in 
concurrence with all the other weights Q, which defcend 
at the fame time. This wheel, A B, carries beneath it 
oblique or bevelled teeth, GD, which take in a like 
wheel, C E, and caufe the buckets at SS to rife. 
From the preceding defcription, it is feen that the ma¬ 
chine being fuppofed to ftart from a ftate of repofe, the 
wind will at firft raife a number of weights, Q, lufficient 
to put the machine into motion, and will continue to raife 
new weights, whilft thofe before raifed are fallen, fo that 
the motion once impreffed will be continued. 
Among the numerous advantages of this mechanifm, 
the following may be remarked : j. No violent Ihock can 
take place in any part of the mechanifm. 2. The ufeful 
effedt being proportioned to the number of weights Q, 
Which defcend at the fame time, this effedt will iricreafe 
in proportion as the wind becomes ftronger, and caufes 
the fails to turn with greater velocity. 3. The weights, 
Q, being moveable along the levers F G, it will always be 
very ealy to place them in fuch a manner as to obtain 
that 
