Henry Moseley.

Syllabus of a course of experimental lectures on the Theory of Equilibrium, to be delivered at the King's College, London, in the October term of the year 1831 online

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Online LibraryHenry MoseleySyllabus of a course of experimental lectures on the Theory of Equilibrium, to be delivered at the King's College, London, in the October term of the year 1831 → online text (page 1 of 2)
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TJiese Lectures require no introductory course of
mathematical reading; the method of demonstration
being exclusively experimental.




&c. &c.

Time Space, — Matter Force,

On the nature of a Property or Quality.

The Properties of Matter, — Impenetrability —
uselessness of the term, as simply implying the
distinction of matter and space. — Divisibility.

Molecules, — Quantity, — Motion, — Force. —
Quantity of motion, — Velocity, — Direction Resist-
ance, — Pressure, — Equilibrium,

All the mutual relations of Time — Space —
Matter — and Force, belong properly to the science
of Mechanics.


" 090

According to the usual acceptation of the term.
Mechanics, that science is, however, confined to the
investigation of the conditioms of the equilibrium
and the rnotiori of masses, or aggregates of matter,
acted upon hy known and appreciable forces.

To the theory of Equilibriwn belong — the science
of Statics, or the Equilibriwn of Solids — and the
science of Hydrostatics, or the Equilibrium of

To the tJieory of Motion belong — the science of
Dynamics, or the Motion of Solids — and of Hy-
dronamics, or the Motion of Fluids,

On the Abstract or Mathematical Method in

On the Experimental Method — Nature and limits
of the proof by experiment.



Substitution of the term pressure for force in
Statics, as implying force held in equilibrium.
The equality of pressures.
The unit of pressure.
The quantity of pressure-

The direction of pressure.

The representation of pressures, in quantity and
direction, by lines.

Forces, to sustain one another upon a flexible line,
must be equal ; act from one another, and in the
direction of the line, at the points where they are
applied to it. These conditions being satisfied, the
form of the line is immaterial, and the pressures
may be any where appHed in it.

Application of pressure by means of the cord and

If any number of pressures, acting upon the
parts of a rigid system, are in equilibrium among
themselves, and if to the same system there be
applied other pressures, such as do not disturb the
equilibrium thus existing ; these last are in equili-
brium amongst themselves.

Difficulty of ascertaining the conditions of the
equilibrium of given pressures applied to a rigid
system, arising from the impossibility of obtaining
any such system not already acted upon by the
pressure of gravity, or weight.

This difficulty obviated by placing the system in
equilibrium with respect to that pressure.

On the equilibrium of two j^i'^'s^^^fc's acting upon


a rigid system, — They must be equal — they must
act in opposite directions, but in the same straight
line. These conditions being satisfied, the form of
the system and the points of application of the
pressures may be any whatever, and they may act
either to or from one another.

Pressure is propagated through rigid bodies in
right lines.

On the equilibrium of three pressures in the
same plane acting upon a point.

The parallelogram of forces.

The equilibrium of a weight suspended by two
cords. '

The resistance of a surface is in a direction per-
pendicular to that surface.

The equilibrium of three pressures, one of which
is supplied by the resistance of an inclined plane,
or a curved surface.

The equilibrium of a weight upon an inclined
plane — when the power acts (1st) parallel to the
surface of the plane — (2d) parallel to its base —
(3d) at any angle above the plane — (4th) at any
angle below it.

The force required to retain the plane at rest,
when acted on by given forces.

The wedge when it is in equilibrium. — The

The equilibrium of weights sustaining one another
on two inclined planes, by means of a string passing
over a pulley.

The equilibrium of weights sustaining one another,
as above, on two curved surfaces.

On curves of equilibration.

The equilibrium of any number of pressures
acting, in the same plane, upon a point.

The polygon of forces.

The equilibrium of three pressures in different
planes, acting upon a point.

The equilibrium of any number of pressures in
different planes, acting upon a point.

The equilibrium of three pressures acting uj)on
a rigid system in the same plane.

Case in which the three pressures are parallel.

Case in which one of the pressures is supplied by
the resistance of a fixed axis, about which the sys-
tem is moveable.

Pressure upon the axis.

Conditions of equilibrium in the case in which the
forces are parallel — deduced from the above — proved


The straight lever (1st) when the forces are ob-
lique, — (2d) when they are parallel. The balance. —
The false balance — means of weighing correctly with
it. — The steelyard. — The handspike. — The crooked
lever. — The crooked balance. — The hammer lever. —
The crank. — Combinations of levers. — The weighing
machine. — The Russel press lever. — The Stanhope
press lever. — The genou.

The wheel and axle. — The capstan. — The fusee.
The cog-wheel.— Pinion. — Trundle. The forms of
the cogs, leaves, and staves of these, necessary to an
uniform action of the machinery. Precautions as
to form, &c. may be in a great measure neglected,
where the cogs are small. — System of toothed
wheels. — The crane.

The screw— the relation of the power and weight
independent of the diameter of the screw. — The
endless screw. — Hunter's screw. — Combinations of
the screw and lever. — The camb.

The pulley. — The single moveable pulley. —
Smeaton's pulley. — White's pulley. — The Spanish
burton. — The system of pulleys in which the last
supports the weight. — The system of pulleys in
which each string is attached to the weight. —
The American burton.


Different mechanical contrivances for varying the
quantity and direction of pressure and motion. —
The crank. — Crown, spur and bevelled wheels. —
Hook's joint. — Parallel motions. — The sun and
planet wheels^ &c. — The eccentric.

The equilibrium of any number of forces in tJie
same plane applied to a rigid system.

Lemma, — I-f there be a parallelogram in a given
plane, and a point be anywhere taken in the same
plane ; the difference of the areas of the triangles
formed by drawing lines from the given point to the
extremities of two adjacent sides of the parallelo-
gram, shall be equal to the area of the triangle
formed by lines drawn from the given point to the
extremities of the diagonal.

Theory of areas.

Theory of moments.

Case in which the system revolves upon an axis
perpendicular to the plane of the forces.

Pressure upon the axis.

Equilibrium of any number of parallel forces
acting upon a rigid system in the same plane.

Equilibrium of any number of parallel forces
acting any where upon a rigid system.

The centre of gravity.


Examples, — the centre of gravity of a parallelo-
gram — of a triangle — of a pyramid — of a prism — of
a circle — of a semicircle — of a parabola — of a cycloid.

Conditions of the equilibrium of a heavy body
sustained on a horizontal plane — on an inclined
plane — and on a curved surface. — (1) When the
base of the body is a plane. — (2) When the base is
a curved surface.

The hanging tov/ers of Pisa and Bologna.

Comparative stability of structures of different

Theory of the carriage v^^heel. — The drawbridge.

Stability of loaded vehicles.

Guldinus's properties.

The centre of gravity of a body or system of
bodies, in equilibrium, is at its highest or lowest
possible point. This proposition proved generally.
— Exemplified in the case of the inclined plane. —
The crooked lever, &c.

The equilibrium of a beam supported upon a
roller and a vertical plane^ — of a rectangle upon
two rollers — of a beam upon two surfaces.

The equilibrium of a beam supported by a string
fastened at its extremities — supported by two
strings passing over pulleys, and carrying weights.


The position of the centre of gravity in animals.
The attitudes of animals dependent upon the
position of the centre of gravity.

TJie conditions of stable — unstable — aud mixed

Examples. — A hemisphere and a parabolid upon a
plane surface. — The same upon a spherical surface.

The common balance— its sensibility — the rapi-
dity of its vibrations — its adjustments. These
require to be different for every different loading,
in order that the sensibility may be greatest of
which the balance is capable.

The equilibrium of a body, or system of bodies,
stable or unstable, according as the centre of
gravity is at its low^est or highest point.

Conditions of the equilibrium of any number of
forces acting, in any given number of directions,
upon a system of invariable form.

Case in which any number of forces act in dif-
ferent directions perpendicular to a rigid line.

Case in which a system acted upon by any
number of forces is moveable about a fixed axis.

Pressure upon the axis.

Conditions of the equilibrium of any number of
forces acting upon a system of variable form.


The jointed polygon of r^ocls.

The equilibrium of a frame-work of two or more
jointed polygons of rods connected together.

The conditions of the equilibrium of a jointed
frame-work loaded with weights, and placed in an
upright position, is the same as though the frame
were suspended and the same loading applied.

Stability of its equilibrium when suspended.

Instability in the opposite position.

Easy practical method of determining the proper
form of a roof, bridge, or other jointed frame under
a given loading ; and the pressure, on its different
parts and its abutments.

Equilibrium of the arch with polished voussoirs.

Instability of its equilibrium.

On tlie equilibrium of the funicidar polygon. —
Case in which the pressures are applied to rings,
moving freely on the thread. — The elastic polygon.

The equilibrium of the funicular curve. — The
common catenary. — The tension on the catenary
at the lowest point varies as the radius of curvature
at that point. — Easy method of ascertaining the
tension at any other point.

On the position of equilibrium of a string of a
given length, suspended over two given points.


On the relation between the length of the string
and the tension on its parts when suspended.

On the positions of equilibrium of a string whose
extremities hang freely over two pulleys, in the
same horizontal line.

Of all the curves, of given length, which can be
drawn so as to terminate in two given points, in
the same horizontal line, the catenary is that whose
centre of gravity is most distant from that line.

On the catenary loaded with weights.— A catenary
may be so loaded as to assume any required form.

Variation in the tension of the catenary, produced
by an irregularity in its loading, and consequent
variation in its form.

The catenary approximates at its vertex very
nearly to a parabola.


The statical laws of friction,

Rennie's apparatus and experiments.

The friction of hard metals under pressures of
less than 32lbs. 8oz. the square inch, nearly one-
sixth of the pressure.

With higher pressures this ratio increases.

The friction of woods.


The friction of stones.

The diminution of friction by unguents, varies as
the insistant weights and the nature of the un-
guents; the lighter the weight, the finer and more
fluent should be the unguent, and vice versa.

On the modifications introduced hy friction in
the conditions of the equilibrium of tJie different
mechanical 'powers.

On the two states bordering upon motion in the
inclined plane.

The wheel and axle.

Methods of diminishing friction by means of fric-
tion wheels. — Friction of the carriage wheel. — The
screw. — The system of toothed wheels.


Coulomb's experiments.

States bordering on motion in the different sys-
tems of pulleys. — The proper ratios of the wheels,
axles, and cords of the different pulleys of each


Absolute resistance. — Rennie's experiments.— The
resistance of different masses of metal, wood, and


stone to the compression of their parts in given
directions. — The resistance of different masses of
metal and wood to the separation of their parts in
given directions. — Anomalous results.

On the strain w^hich produces permanent altera-
tion of structure.— There is reason to believe that
all bodies are perfectly elastic, as to any pressure
less than that which produces permanent alteration
of structure.

Galileo's hypothesis of the rigidity of fibres. —
Leibnitz's hypothesis of the extensibility of fibres. —
Theory which admits the compressibility as well as
the extensibility of fibres.

Relative resistance. — The neutral line — its pro-

On the strength of a horizontal bar fixed im-
moveably at one end, and carrying a weight at the

On the strength of a bar fixed immoveably at
both ends, and carrying a weight between.

On the strength of a bar supported in the middle^
and carrying weights at the ends.

On the strength of a bar carrying weights
variously distributed over its surface.

On the strongest forms of beams.


On the construction of open beams.

On the deflexion of beams by their own weight,
when supported horizontally at their extremities —
when inclined to the horizon.

On the deflexion of columns sustaining weights.

On the proper forms of columns sustaining

The elasticity of flexure.

On the deflexion of elastic laminae.

The equilibrium of springs.

The elasticity of torsion.

On the proper forms , and tlie strength of solid
arches of wood and iron.

On the loading of solid arches.

On the strength of open arches.


The Shed Roof

The angle of its elevation dependent on the height
and the strength of the walls or pillars on which it
abuts. — The strength of its timbers. — Ingenious
method of getting rid of the horizontal thrust, by
supporting the timbers beneath their centres of

TJie commonTruss Roof — The theory of this roof.


— The horizontal thrust on its abutments. — The
different pressures upon its parts, and the consequent
variation in the strength of its timbers.

The deflexions in the tie beam and principal

The variations in the lengths of the timbers.

The strength of the joints.

On the different forms of the trussed roof

Examples, — The roof of the Bazilica of St. Paul's
at Rome. — The roof of the Theatre Argentina at
Rome. — The roof of the Birmingham Theatre.

Methods of giving support to roofs — by means of
additional frame-work abutting in the wall beneath
the tie beam — by means of buttresses, &c.

On truncated roofs.

The roof of Drury Lane Theatre.

On the loading of roofs, hy the suspension of
ceilings, S^c,

The roof and ceiling of the Teatro Alia Scala.

On various methods of dispensing with the tie
beam at the foot of the rafters.

The collar beam — great objections to its use
unless supported by pillars, or otherwise, at its

Roof of the Church St. Genevieve at Paris.



Roof of the Theatre Odeon.

The roof of a church in Wiltshire.

On g'othic roofs.

The roof of Westminster School.

The roof of the Middle Temple Hall.

The roof of Westminster Hall.

On the polygonal roof.

Roofs formed with four principal rafters.

Conditions of he equilibrium of four such raf-

The roof of the Theatre at Bordeaux.

Roofs of sheds in the Arsenal at Cherbourg.

Roofs of sheds in the Dockyard at Plymouth.

The roof of the shed for containing Mahogany in
the West India Docks.

Method of supporting roofs hymeans of polygonal
frames or arches of short rafters.

Great advantages of this method of support.

The proper form and strength of the polygon.

The roof of the Riding House at Moscow^

On the arch of curved timber.

On the use of iron in the framing of roofs.

The roof of the Brunswick Theatre

Roof at Mr. Maudeslay's manufactory.

On trussed floors.


Example.— The trussed floor in the Teatro Alla-
scala at Milan.


The wooden bridge in which the timbers are
straight, and rest immediately upon the piers.

The bridge of Caesar over the Rhine.

The bridge of Cayuga in America.

Method of constructing a wooden bridge over a
rapid torrent.

The bridge across the rapids of Niagara.

On the straight wooden bridge where the timbers
of the roadway are trussed from above, and there
is no horizontal pressure upon the abutments.

The bridge of Palladio over the Cismone.

The great bridge formerly at SchafFhausen.

Wooden bridge near Baltimore, N. America.

The wooden bridge, in which the roadway is
principally supported yrow? beneath by timbers, which
rest obliquely upon the abutments.

The bridge over the Kendal near Berne.

On wooden bridges supported by polygonal

The wooden bridge at Lyons.

On wooden bridges with curved ribs.
B 2


The bridge of Trajan over the Danube.

The bridge of Freysingen in Bavaria.

The bridge of Bamburgh on the Regnitz in

The great wooden arch at Scuykill, in N. America.

The proper variation in the strength of the parts
of the curve of a wooden arch.


Strength requisite in the different portions of the
arch. — Colebrook-Dale bridge. — Buildwas bridge. —
Sunderland bridge. — Bonar bridge. — The bridge
of the Louvre. — Vauxhall bridge. — Southwark
bridge. — Telford's proposed bridge over the


Application of the theory of the loaded cate-
nary. — The method of constructing the chain. —
Easy practical method of determining the tension. —
It is less at the vertex as the curvature is greater.

On the method of suspending the roadway. — On
the piers of the bridge, and the attachment of the
chain. — The wire bridge over the Tees near
Durham. — The wire bridge over the Tweed near


Peebles. — The Kelso suspension bridge. — The sus-
pension pier at Leith. — Brunell's suspension bridge
erected in the Island of Bourbon. — The suspension
bridges over the Cataracts of Sckuylkill, and at
Merimac, in North America. — The Hammersmith
suspension bridge. — The Menai suspension bridge.

Any jointed polygon, or arch, placed in an upright
position so as to be sustained by the pressure of its
parts upon one another and upon its abutments, is
in a position of unstable equilibrium, the centre of
gravity being at its highest possible point. To the
stability of such a polygon, or arch, it is therefore
necessary that its joints should be rendered rigid, in
the directions in v^^hich their position is liable to
disturbance, — by additional framing or otherwise.

In the suspended polygon, or curve, the equili-
brium is stable, the centre of gravity being at its
lowest possible point. There is therefore no neces-
sity for rendering the joints rigid ; and the material,
requisite in the other case for producing this rigi-
dity, may be here dispensed with.

The advantage of the upright over the suspended
arch of the same materials, lies in this, that in
the former case the arch is sustained by the resis-
tance of its parts to compression, and in the latter


by their resistance to separation, and that mate-
rials are torn asunder more readily than they are


True theory of the arch, allowing for the friction
of the voussoirs.

General conditions of the stability of the arch.

The two states bordering upon motion.

Method of describing the line of the least loading
necessary to the equilibrium of an arch whose key-
stone is given.

Line of the greatest loading which such an arch
will bear.

On the comparative strength of different por-
tions of the arch. Generally the strength of an
arch is greater as its curvature is less.

The curvature being given, the stability of an
arch properly constructed increases with the loading.

On the line of pressure.

When the voussoirs are exceedingly narrow, and
the loading considerable, the curve of equilibrium is
the catenary.

Different steps in the fall of an arch.

Example, — Pont y Prydd.


The circular arch.

Easy method of describing the lines of greatest
and least practicable loading.

The great strength of the circular arch, and
variety of loading under which conditions of its
equilibrium obtain.

The segment of a semi-circular arch.

Its advantages over the whole semicircular arch.

No semicircular arch can be safely constructed
with equal voussoirs — A segment may.

A straight wall of any height may be built over
a segment of a circular arch.

Exarnjdes of circular arches.

The bridge of Rimini.

The aqueduct bridge at Nismes.

The bridge of Avignon.

The bridge of Briande.

The bridge of Ulm, &c. &c.

The elliptical arch.

Method of describing the lines of loading in the
two states bordering upon motion, and for given
dimensions of the key-stone.

Weights which an elliptical arch of given dimen-
sions is capable of sustaining on its crown.


Comparative weakness of the semi - elliptical

Cases of semi-elliptical arches, in which, under
the irregular pressures to which they are subjected,
their stability must be dependent upon other causes
than the friction of their parts.

Examples of elliptical arches.

Bridge of the Rialto at Venice.

Bridge over the Arno at Florence.

Bridge of Neuilly.

Waterloo bridge.

London bridge.

On segments of elliptical arches.

Advantages in the use of segments raised upon
high vertical piers, where a clear water way is

A segment of an elliptical arch may be built with
equal voussoirs.

The loading on certain points about the haunches
of a semi-elliptical arch may be any whatever.

Examples of flat arches.
Bridge over the Oise.
Pont de la Concorde.


The arch between the western towers of Lincoln

On the pointed gothic arch.

Equilibrium of the pointed arch.

Method of determining the states bordering upon

The loading of the key-stone.

Comparative strength of the varieties of the
pointed arch.

Conditions of the equilibrium of an arch, taking
into account the tenacity of the cement.

On the piers of arches.

On the centering of arches.

On the equilihrium of the dome.

The weight on the haunches may be increased
without limit, and their convexity diminished, but
not the contrary.

A dome may be built w^ithout centering. — Ex-
ample, — The dome of the cathedral of Florence.

On the equilibrium of a dome loaded on the
crown — The domes of the cathedral at Florence, St.
Peter's of Rome, and St. Paul's in London. — On
^he equilibrium of a dome in which the crown is


On the theory of the groin.
On the conoidal groin,


Lagrange's proof.

The principle of virtual velocities shewn to obtain
in the following cases of equilibrium.

The equilibrium of any number of forces acting
upon a point. — Of weights on the straight lever. — Of
forces acting obliquely on the crooked lever. — In
the case of the single pulley where the strings are
inclined. — Of a system of compound levers. — Of the
inclined plane. — Of equilibrium on a curve — on two
curves — of the screw — of the wheel and axle — of
toothed wheels, &c. &c. — In the case of motion about
the centre of gravity of any system of bodies.

The centre of gravity of any system of weights
is at its highest or lowest points, when those weights
are in equilibrium— proof deduced from the prin-
ciple of virtual velocities.

On the quantity of motion.

The quantity of motion, a measure of the moving

Demonstration of the principle of virtual velocities
founded on this consideration.




Online LibraryHenry MoseleySyllabus of a course of experimental lectures on the Theory of Equilibrium, to be delivered at the King's College, London, in the October term of the year 1831 → online text (page 1 of 2)