"Why then firstly, lord, firstly we have the great Mangon or mangonel, fundis fundibula, that some do also term catapultum, the which worketh by torsion and shall heave you great stones of the bigness of a man fully two hundred yards an it be dry weather; next is the Trebuchet, like to the mangon save that it swingeth by counterpoise; next cometh the Balista or Springald that worketh by tensiona pretty weapon!

<Tort> (twist): (1) torture, tortoise, retort, contort, distortion, extortionate, torch, (apple) tart, truss, nasturtium; (2) tort, tortuous, torsion, Dry Tortugas.

At the beginning and end of the stroke when the crank is vertical, no force of torsion can be exerted on the crank shaft by the crank, but this force is at its maximum when the crank is horizontal.

From the vertical point, where this force is nothing, to the horizontal point, where it is at its maximum, the force of torsion exerted on the crank shaft is constantly varying; and the fly wheel by its momentum redresses these irregularities, and carries the crank through that "dead point," as it is termed, where the piston cannot impart any rotative force.

In screw vessels the thrust will be determined by the force turning round the screw, and by the smallness of the screw's pitch; for with any given force of torsion a fine pitch of screw will give a greater thrust than a coarse pitch of screw, just as is the case when a screw works in a solid nut.

Kent's Torsion Balance.

* KENT'S TORSION BALANCE.

The United States Torsion Balance Company, of New York, has recently brought before the public a new form of balance which presents so many ingenious and excellent features that we illustrate it below, on the present page.

[Illustration: KENT'S TORSION BALANCE.

[Illustration: KENT'S TORSION BALANCE.

In spite of all the foregoing facts, it was reserved for the "Encyclopedia Britannica," in its ninth edition, to use the following as the result of its condensed wisdom: "In the torsion balance proper, the wire is stretched out horizontally, and supports a beam so fixed that the wire passes through the center of gravity.

" [Illustration: KENT'S TORSION BALANCE.

On the contrary, the torsion balance seems very much alive.

One of the first forms of the torsion balance which met the disapproval of the "Encyclopedia Britannica" was attended with the difficulty that the pivoted wires were attached directly to the bifurcated ends of the beam, and could not be tensioned without bending these ends unless the beam was made so heavy as to interfere with its employment in delicate weighing.

[Illustration: KENT'S TORSION BALANCE.

[Illustration: KENT'S TORSION BALANCE.

For ordinary balances on the torsion system, in which extreme sensitiveness is not needed, the trouble caused by change of level of the scale is insignificant; but it becomes a matter of importance in more sensitive scales, such as fine analytical balances in places where it is impossible to keep the table or support of the scale level, for instance on shipboard.

It is applied in those varieties of the torsion balance in which there are two parallel beams, connected by either four or six wires.

TORSION TEST

[Footnote 64: Wood is so seldom subjected to a pure stress of this kind that the torsion test is usually omitted.

] Apparatus: The torsion test is made in a Riehle-Miller torsional testing machine or its equivalent.

49.Making a torsion test on hickory.]

Results: The conditions of ultimate rupture due to torsion appear not to be governed by definite mathematical laws; but where the material is not overstrained, laws may be assumed which are sufficiently exact for practical cases.

M = moment of torsion at elastic limit, inch-pounds.

112-121. BOUNICEAU,: Note et expériences sur la torsion des bois.