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NATURAL PHILOSOPHY. so attached as to give rapidity of motion at the ex

pense of power. The ox-yoke is of this kind, the MECHANICAL POWERS.

neck of each ox being the fulcrum with reference to

the exertion of the other. The stronger of two By the mechanical powers are signified the simple oxen must have the short arm of the lever, that they machines to which all machines, however complex, may be able to pull together. So a load supported may be referred. They are essentially three in on a pole and borne by two men must divide the pole number, but usually considered as six:

unequally, if either is to be favoured. The mechan. I. The LEVER and the WHEEL and axis.

ical advantage may be multiplied to any extent by a II. The INCLINED PLANE, the SCREW, the WEDGE. combination of levers of the first kind. Such a III. The PULLEY.

combination is used to prove the strength of iron cables. To the lever are referred the various instruments employed for weighing. The inost perfect of these is the common balance. For entire accuracy, the arms should be of precisely the same length, and as nearly as possible inflexible, light,

The axis on which it turns, and the points of suspension at the ends of the arms, should be sharp, and rest upon polished plates of steel.

The accompanying figure represents a combina

tion of levers in which great power is obtained. It The lever is a bar, resting on a support, called 'a is intended for pressing and cutting of metal. The fulcrum or prop, for the purpose of raising, by a principal lever, placed power applied to one end, a weight at the other. An at the top of the mairon crow, used by workmen to raise heavy stones, chine, revolves on the affords a good instance of a lever. The stone is the axis or fulcrum e, weight; the block on which the crow rests is the which must be imfulcrum; the strength of the men, the power. To moveable and of great gain any advantage by its use, the fulcrum must be strength. The point nearer to the weight ihan to the power. If the dis-b is just three times tance from the power to the fulcrum be five times as far from the axis greater than the distance from the weight to the ful- a as the pressing orcrum, a force of one pound in the power will bal- | ifice is. A rod de ance a pressure of five pounds in the weight. But scends from the point in this case the end of the long arm of the leverb, and carries the mechanical advantage thus obtainwill, as it turns on the prop, pass through a space ed to the lever beneath, and, as that turns on an axis five times greater than that of the short arm. By placed at the extremity, a pressing power applied at such a lever a man could raise one thousand pounds the end of the longer arm d will act with an amazing with the same exertion as would be required to raise force on the cutting part of the machine. 'The two hundred without a lever, but he could raise it weight e is intended merely to raise the levers after only a fifth part so high in the same time. What the power is withdrawn. he would gain therefore in power would be lost in The wheel and axle consist of a wheel attached lo time. In theory, a lever is considered inflexible and a smaller cylinder, and moving on the same axis. without weight. There is an equilibrium when the The weight to be raised has a cord winding round power and weight are inversely as their distances the cylinder, and the power is attached to the cirfrom the fulcrum.

cumference of the wheel. It may be regarded as a Leverage is the distance of the power from the continual lever, each spoke of the wheel represent

The mechanical advantage or purchase is ing the long arm, and the radius of the cylinder the proportional to this distance compared with that of short arm. The mechanical advantage depends on the weight from the fulcrum. Levers are of three the ratio of the cylinder. In the ship's windlass, kinds, according to the relative position of the pow- moveable bars or handspikes are substituted for a er, the prop, and the weight.' In the first, the prop wheel. The capstan is a vertical wheel and axle is between the power and the weight. To it belong used on board ships to weigh the anchor. scissors, snuffers, pincers, (in which the pivot or The wheel and axle may turn on different cenjoint is the prop,) the handspike, the brake of a tres, and have their circumferences connected and pump, &c. A hammer with its claw is a bent lever made to act on each other, by means of a strap or of this kind. In the second, the weight lies between belt, or by a system of cogs or teeth. 'The latter the fulcrum and the power. This includes the oar, plan is adopted in this arrangement, and is called where the boat is the weight to be moved ; the door, wheel and pinion work. of which the hinge is the fulcrum; the wheelbarrow, nut-crackers, bellows, and the knife attached at one end, used to chip die-woods. In a lever of the third kind, the resistance is at one end and the fulcrum at the other. To this belong the pitchfork and spade, the one end being the power and the other the fulcrum, sheep-shears, with a bow at one end, giving a greater facility of motion. The bones of animals are levers of this kind, and are moved by muscles

VOL V.42

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The weight to be raised is supported by a flexible cask, he employs the principle of the inclined plane, cord coiled round the axis a; and, as the teeth of and the more gradual the inclination of the plank the wheel are three times as far from the centre as the more easily will he effect his purpose : that is the cord, one pound will raise three pounds. In the the advantage gained by the inelined plane is greater wheel and pinion eb, a similar advantage is obtained, the more the length of the plane exceeds its height. and nine pounds may be elevated. Passing on to A road which is not level is an inclined plane the third in the series, twenty-seven pounds may be When a road mounts over a hill, instead of winding raised by a maintaining power of one pound applied round its foot, a team of horses with a load of a tun by the hand.

weight must exert strength sufficient to lift the load Another example, and a still more striking one, is perpendicularly into the air, to a height equal to that given in the wheel and axis abcd. The power is of the top of the hill, instead of that moderate exin the first instance applied at the handle a, which ertion which is necessary to overcome the friction acts on the screw bc with great force. The screw of the axis of the wagon and the slight inequalities turns the wheel d, and that gives motion to the small of a level road. Hence the absurdity of constructbarrel. The handle at a will raise a weight of ten ing roads in hilly countries to pass directly over the pounds at the screw, and, if that make forty revolu- tops of hills, instead of winding by small circuits tions to one of the wheel, four hundred pounds may along their base. A body descending freely on an be raised. It may hardly be necessary to add that, inclined plane moves with a velocity as much less as the barrel is smaller than the wheel, the mechan-than that with which it falls freely as the height of ical advantage is proportionably increased. the plane is less than the length. If the elevation

were one sixteenth of the length, the body would roll down one foot in the first second, and four in twice that time. It is on this principle that the equality in the vibrations of a pendulum may be explained. A long vibration takes no more time ihan a short one, because the body begins to fall in this case down a steep plane, and acquires great relocity. In a short vibration, the beginning of its path is a very gradual descent. A short pendulum vibrates more rapidly than a long one, because it has a shorter distance to move in a path of the same steepness. A body moving down an inclined plane

moves four times as far in two seconds as in one stelde

A pendulum, to vibrate once in two seconds, must

be therefore four times as long as one which beats The efficacy of the wheel and axle may be in- seconds. The most remarkable application of the creased either by enlarging the diameter of the wheel inclined plane is in the construction of the marine or diminishing that of the cylinder.

railway, on which, by the power of a few horses, a 7- The Chinese capstan furnishes the means of in- ship of six hundred tuns is drawn, with all its cargo, creasing the mechanical efficacy to any degree. It out of the water, high enough to allow workmen to consists of two cylinders of nearly equal diameters, pass under its keel. turning upon the same axis, the weight being sup- The inclined plaue is one of the three mechaniported by the loup of a very long cord, one end of cal powers, or simple machines, formed, as its name which unwinds from the smaller cylinder, while the imports, by a plane surface, supposed to be perfectly other end is coiled upon the larger. The elevation hard and inflexible, and which is always inclined of the weight by each revolution is equal to half the obliquely to the weight or resistance to be overcome. difference of the two circumferences, the mechan. The wedge is a modification of this machine, being ical advantage depending upon the smallness of this formed of two inclined planes placed base to base. difference.

The screw is another modification, being, in fact, An arrangement of

merely an inclined plane wound round a cylinder. this kind is shown in

This machine enables us to raise a given weight the accompanying fig.

along the inclined surface to a given elevation, with ure. One end of the

less expense of force than would be required to raise cord coils round the

it perpendicularly to the same elevation. The perfirst cylinder, and de

pendicular height is called the elevation of the plane, scending passes under

and the two lines enclosing the angle which it subthe pulley to which

tends are called the base and the length of the plane. the weight is attached. It is then carried around the smallest eylinder, and the apparatus may either be made to draw in a horizontal or vertical direction.

Inclined plane. - When a carman lays a plank from the street to the higher level of the floor of a There are two modes of exhibiting the power of the store-house, that he may be able to roll in a heavy l inclined plane. The arrangement exhibited above

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consists of three paths, inclined to the planet. The screw with its handle A, and grooved pulley of the horizon at different angles. To carry a B, works in the teeth of the wheel D. Now if we loaded carriage up the first would require a weight suppose forty-eight teeth in the wheel, it must be of one pound, the second two pounds, and the steep- obvious that, for every time the pulley B and the est plane three pounds. If the inclined path be screw are turned round by the winch A, the wheel three times the length of the perpendicular lift, it will be moved one tooth by the screw; and there-will require only one third the weight to raise the fore, in forty-eight revolutions of the winch, the carriage, but then it will require three times as long wheel D. will be turned once round. Then, if the to accomplish the work.

circumference of a circle, described by the handle In the second arrangement of the inclined plane, of the winch A, be equal to the circumference of a the mechanical advantage is precisely the same, but groove round the pulley B, the velocity of the hanthe plane itself is put in motion. This is in reality dle will be forty-eight times as great as the velocity the operating power in a common screw.

of any given point in the groove. Consequently, if a line G goes round the groove, and has a weight of forty-eight pounds hung to it, a power equal to one. pound at the handle will balance and support the weight. To prove this by experiment, let the circumferences of the grooves of the wheels B and D be equal to one another; and then, if a weight of

one pound be suspended by a line going round the The Screw. Imagine an inclined plane to pass groove of the wheel, it will balance a weight of. round an immense building like the tower of Babel, forty-eight pounds hanging by the line G; and a affording means of ascending to the top, and you small addition to the weight Ċ will cause it to dehave the first idea of the screw. It is an inclined scend, and so raise up the other weight. plane wrapped spirally round a solid cylinder. The If a line G, instead of going round the groove of advantage gained by it depends on the slowness of the wheel D, goes round its axle I, the power of the the ascent, that is, on the number of turns, or machine will be as much increased as the circumthreads as they are called, in a given distance. It ference of the groove exceeds the circumference of is always used in combination with a lever. It is a the axis : supposing it to be six times, then one machine of great power, commonly employed to pro-pound at C will balance six times forty-eight, or two. duce compression or to raise heavy weights. In hundred and eighty-eight pounds hung to the line ou the screw beneath, the threads which form the path the axis : and hence the power or advantage of this of the inclined plane are flat, instead of being sharp machine will be as two hundred and eighty-eight to as in the common wood screw, and this form is well one. That is to say, a man, who by his natural fitted for heavy work, as it materially reduces the strength could lift a hundred weight, will be able to friction.

raise two hundred and eighty-eight hundred weight by this engine. If a system of pulleys were applied to the .cord C, the power would be increased to an amazing degree.

When a screw acts in a wheel in this manner, it is called an endless screw.

The Archimedean screw is a machine for raising water, which consists either of a pipe wound spirally round a cylinder, or of one or more spiral excavations formed by means of spiral projections, from an internal cylinder, covered by an external coating, so as to be water-tight. The arrangement of the apparatus may be thus familiarly illustrated. If we conceive a flexible tube to be rolled regularly about a cylinder from one end to the other, the tube or canal will be a screw or spiral, in which we suppose the intervals of the spires or threads to be equal. The cylinder being placed with its axis in a

vertical position, if we put in at the upper end of A machine is sometimes constructed so as to show the spiral tube a small ball of heavy matter, which the precise power of a screw when combined with

may move freely, it is certain that it will follow all a wheel and axis, or lever, as in the cut below.

the turnings of the screw from the top to the bottom of the cylinder, descending always as it would have done had it fallen in a right line along the axis of the cylinder, except that it will occupy more tiine in running through the spiral. If the cylinder be placed with its axis horizontally, and we again put the ball into one opening of the canal, it will descend, following the direction of the first demispire ; but, when it arrives at the lowest point of this portion of the tube, it will stop. It must be remarked that, though its gravity has no other tendency than to make its deseqnt in the demispire, the oblique

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position of the tube, with respect to the horizon, is termined by the obliquity of the position of the cyl.
the cause that the ball, by always descending, is inder.
always advancing from the extremity of the cylinder Instead of the ball, let us now consider water as
whence it commenced its motions to the other ex- entering by the lower extremity of the spiral canal,
tremity. It is impossible that the ball can ever ad- when immersed in a reservoir, as is shown in the
vance more toward the further, or, as we shall call accompanying figure.
it, the second extremity of the cylinder, if the cyl- This water descends first in the canal solely by
inder, placed horizontally, remain always immovea- its gravity, but the cylinder being turned, the water
ble; but if, when the ball has arrived at the bottom moves on through the canal to occupy the lowest
of the first demispire, we cause the cylinder to turn place, and thus, by the continual rotation, is made
on its axis without changing the position of that to advance further and further in the spiral, till at
axis, and in such a manner that the lowest part of length it is raised to the upper extremity of the ca
the demispire on which the ball presses becomes nal, where it is expelled.
elevated, then the ball falls necessarily from that There is, however, with reference to the com-
point upon that which succeeds, and which then be puted effect of this machine, an important difference
comes lowest ; and, since this second point is more between the water, or any other fluid, and the ball;
advanced toward the second extremity of the cylin-1 for the water, by reason of its fluidity, after having
der than the former was, the ball will, by this new descended by its gravity to the lowest point of the
descent, be advanced toward that extremity, and so demnispire, rises up on the contrary side to the ori-
on throughout, in such a manner that it will at length ginal level; on which account more than half one of
arrive at the second extremity by always descend- the spires will soon be filled with the fluid. This
ing, the cylinder having its rotatory motion contin- is an important particular, which, although it need
ued. Moreover, the ball, by constantly following not be considered in a popular illustration, must be
its tendency to descend, has advanced through a attended to in a more accurate exhibition of the the-
right line equal to the axis of the cylinder, and this ory of this engine. The very little application of
distance is horizontal,

ause the sides of the cyl- this machine to the purposes it calculated to an-
inder are placed horizontally. But if the cylinder swer, will not, however, justify our entering upon a
had been placed obliquely to the horizon, and we more minute examination of its theory in this place ;
suppose it to be turned on its axis always in the, although we must observe that it seems entitled, in
same direction, it is easy to see that if the first quar- a practical point of view, to greater attention than it
ter of a spire actually descends the ball will move now commonly receives. The Germans have a
from the lower end of the spiral tube, and be car- similar machine, which they call the water-screw;
ried solely by gravity to the lowest point of the first it consists of a cylinder, with its spiral projections
demispire, where, as in the preceding case, it will detached from the external cylinder or coating with-
be abandoned by this point, as it is elevated by the in which it revolves. It is evident that some loss
rotation, and thrown by its gravity upon that which must here be occasioned by the want of perfect con-
has taken its place: whence, as the succeeding tact between the screw and its cover; in general, at
point is further advanced toward the second extrem- least one third of the water runs back, and the ma-
ity of the cylinder than that which the ball occupied chine cannot be placed at a greater elevation than
just before, and is consequently more elevated, 30°; it is also very easily clogged by accidental
therefore the ball, while following its tendency to impurities of the water.
descend by its gravity, will be always more and more

(To be continued in our next.) elevated by virtue of the rotation of the cylinder. It will thus, after a certain number of turns, be advanced from one extremity of the tube to the other, or through the whole length of the cylinder, but it will only be raised through the vertical height de

POPULAR MEDICAL OBSERVATIONS.

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HEREDITARY PECULIARITIES.
That the features, voice, and manner of parents
are often transmitted to their children, is a familiar
fact; though it has not received such an extension
and variety of application as by its importance it is
so well entitled to. For the present, our remarks
will be on those hereditary peculiarities indicated
by genius, infirmities of temper, and tendency to
bodily ailments and disease.

We must here take care not to identify the pos-
session of genius with its determinate and success-
ful display. The same faculties which were allowed
to remain dormant, or which were faintly exhibited
in the parent, may, when transmitted to the child,
and fostered by opportunity and education, with,
perhaps, the additional incentives of self-love and
firmness of purpose, shine out with all the lustre of
successful talent. TO in the father is expanded

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into genius in the son. The same intellectual pow- | unconcern about those things which agitate the ers and peculiarities being possessed by both, the greater part of mankind, and a general sensation of difference will consist in the superiour vigour in the gloomy wretchedness. From him then, continues one over those of the other. We are also to re- the biographer, the son inherited, with some other member, that whatever there is marked in the char- qualities, “a vile melancholy," which, in Johnson's

, acter of either mind or body, will be exhibited in the own too strong expression of any disturbance of the offspring, with modifications depending on the sim- mind, “ made him mad all his life, at least not soilarity or difference, in these particulars, between ber.” Johnson's mother was a woman of distinthe father and mother. This last is an important guished understanding, of whom it was said, in refconsideration, when we desire to solve the problem erence to her probable elation at her son's celebrity, of hereditary qualities.

that although she knew his value, she had too much Notwithstanding the deficiency in so many biog- good sense to be vain of him. The disease of scrofraphies, of details of the peculiar cast of mind, ula or king's evil, under which he suffered in early and tastes of the parents of the subject of the life, so much as to have his countenance disfigured, narrative, we have yet enough to illustrate the he- and to lose the sight of one of his eyes, is erronereditariness of genius. Raphael's father was him- ously referred to contagion from his nurse. self an artist. The mother of Vandyck was distin- part of his inheritance and the direct consequence "guished for painting flowers. The grandfather of of his peculiar bodily frame. In him were seen the eccentrick Benvenuto Cellini was an architect; that precocity of intellect and facility of attainment and his father versed both in architecture and drawn which are so commonly associated with this disease. ing. Or Parmigiano's parents we know little-his Burns, who was constitutionally melancholy and father dying when he was very young ; but both his hypochondriack, derived also from his father a rouncles were painters, and became his preceptors in bust but irritable structure and temperament of body an art in some parts of which he rivalled Correggio and mind. In features and general address, the himself. Vasari's father gave him instructions in poet bore a greater resemblance to his mother, drawing. Vanloo, commonly called the Chevalier From her he inherited that fondness for ballads and Carlo, state painter under Louis XV., and an artist traditionary lore, which was tho germe of his subseof deserved eminence, was the brother, son, grand- quent poetical greatness. son, and great-grandson of painters. Horace Ver- Of Byron's inherited peculiarities we cannot betnet, who ranks among the foremost of the modern ter speak than in the language of his biographer, French school, is the son of Charles Vernet, (fa- Mr. Moore. ""In reviewing," says this writer, "thus mous for his paintings of horses and farmyard scenes, cursorily the ancestors, both near and remote, of in which these animals are the chief figures,) and Lord Byron, it cannot fail to be remarked, how strigrandson of the Joseph Vernet so celebrated for kingly he combined in his own nature some of the his marine views. The brother of this last, though best, and perhaps worst, qualities that lie scattered a bookseller by trade, was fond of painting, which through the various characters of his predecessorshe sometimes practised ; and his pictures have been the generosity, the love of enterprise, the high-mindmistaken for those of Joseph. 'Titian's two young-edness of some of the better spirits of his race, with er brothers, and son and nephew, and grandneph- the irregular passions, the eccentricity, and daring ew were painters. The strong family resemblance recklessness of the world's opinion, that so much of genius is well evidenced in the Caracci, of characterized others.” whom Louis and his three cousins, Augustin, Anni- History furnishes us with no example of a man of bal, and Francis, were the distinguished heads of inventive genius, or large general powers of underthe Bolognese school of painting. Antonio, the son standing, who was born of imbecile parents. We of Augustin, gave early promise of greatness in the are safe in affirming, that they who have figured same line, in which he was arrested by death. In most conspicuously on the great theatre of life, have the sister art of musick, similar instances of this been much indebted to inheritance for that vigour of inheritance and subsequent transmission of genius intellect which has given them the mastery of their might be readily furnished. The father of the tender fellow-beings. Our reference need not extend furMozart was a violinist of reputation ; and the sister ther than to him whose name is identified with the of this celebrated composer displayed as precocious most astonishing changes and revolutions in modern a musical talent as himself. He left two sons, Europe. "The father of Napoleon Bonaparte," says one of whom is a musick director at Lemberg. Sir Walter Scott, “is stated to have possessed a Beethoven was the son of a tenor singer. More very handsome person, a talent for eloquence, and than fifty musical composers have proceeded from a vivacity of intellect, which he transmitted to his the family of John Sebastian Bach a name so cele- son.” And again he remarks~"It was in the midbrated in musical literature.

dle of civil discord, fights, and skirmishes, that Among the examples of inherited bodily infirmi- Charles Bonaparte married Letitia Ramolini, one of ties and peculiarities of intellect and feeling in the most beautiful young women of the island,

and distinguished geniuses of later days, we shall con possessed of a great deal of firmness of character. . tent ourselves with citing Johnson, Burns, and By- She partook of the dangers of her husband during ron. The father of Dr. Johnson was, say Boswell, the years of civil war, and is said to have accompaa man of large and robust body, and of a strong and nied him on horseback on some military expedition, active mind; yet, as in the most solid rocks, veins or perhaps hasty flights, shortly before being delivof unsound substance are often discovered, there cred of the future Emperour.” was in him a mixture of that disease, the nature of Frequent intermarriages among the members of which eludes the most minute inquiry, though the a particular class, as nobility or royalty, is follo:se:? effects are well known to be a weariness of life, an'by a deterioration of mental and physical energi.

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