Torsion balance

“ Astron. di Milano', 1824, p. 184) ; (3.) by the torsion balance used by Cavendish, with an apparatus originally devised by Mitchell, 5.48 (according to Hutton's revision of the calculation, 5.32, and according to that of Eduard Schmidt, 5.52; 'Lehrbuch der Math. Geographie', bd. i., s. 487) ; by the torsion balance, according to Reich, 5.44. ”

“ The theory shows further that the resistance to torsion is very seriously diminished when there is in the surface any dent approaching to a re-entrant angle. At such a place the shearing strain tends to become infinite, and some permanent set is produced by torsion. In the case of a section of any form, the strain and stress are greatest at points on the contour, and these points are in many cases the points of the contour which are nearest to the centroid of the section. ”

“ We have already called attention to the difficulty [27] of the operation of free torsion, which requires a great deal of strength, and which, besides, may be accompanied by a serious inflammatory condition of the parts, through rough manipulations of the cord. It is for this reason that this mode of procedure must have been reserved for small animals, as, if performed upon the larger kinds, it can only be by men whose muscular force is sufficient to enable them to overcome and bring into subjection the struggling subjects of their operations. ”

“ There is one other phenomenon which meets us in the twining and twisted stem, and which is doubtless illustrated also, though not so well, in the antelope’s horn; it is a phenomenon which forms the subject of a second chapter of St Venant’s researches on the effects of torsional strain in elastic bodies. We have already seen how one effect of torsion, in for instance a prism, is to produce strains parallel to the axis, elevating parts and depressing other parts of each transverse section. ”

“ The stress-couples consist of two flexural couples in the two principal planes, and the torsional couple about the tangent to the central-line. The torsional couple is the product of the torsional rigidity and the twist produced; the torsional rigidity is exactly the same as for a straight rod of the same material and section twisted without bending, as in Saint-Venant’s torsion problem (§ 42) . ”

“ December 24.—The patient's condition is more than ever deplorable. On the slightest provocation—indeed, on no provocation at all—furious torsion movements force the head backwards and to the right, while the right shoulder rises. ”

“ Torsion, tor′shun, n. act of twisting or turning a body: the force with which a thread or wire tends to return when twisted, the kind of strain produced in a bar or wire when one end is kept fixed and the other is rotated about the axis: (surg.) a method of common application for the purpose of checking arterial hæmorrhage in certain cases, by twisting the cut end of the artery.—n. ”

“ When these assumptions are made it appears that there is one and only one distribution of shearing stress by which the conditions of the problem can be satisfied. The determination of the amount and direction of this shearing stress, and of the corresponding strains and displacements, was effected by Saint-Venant and R. F. A. Clebsch for a number of forms of section by means of an analysis of the same kind as that employed in the solution of the torsion problem. ”

“ First came a number of torch-bearers, whose duty it was to light the great brush torches that are planted at intervals all down the avenue. These torches are as thick as a man's body and ten feet high; and as they flickered, crackled and then sent up a spire of lurid, smoky flame, they seemed to turn everything blood-red, and made the advancing ranks of the procession look more like a company of fiends than of human beings. ”

“ Tearing differs, then, from torsion only in the fact that after giving several twists to the cord in order to gather its fibres into a more compact mass, and to diminish the resistance of the more superficial layers, it is divided in its continuity by a violent traction upon its fibres in the direction of its length. ”

“ Indirect violence, especially when exerted in such a way as to combine traction with torsion,—for example, when the foot is caught in the spokes of a carriage wheel,—is the commonest cause of epiphysial separation. Direct violence is a much less frequent cause. Muscular action occasionally produces separation of the epiphyses—for example, the anterior superior iliac spine, the small trochanter of the femur, or the upper end of the fibula. ”

“ So a cylinder, which is especially resistant to torsion, is very easily bent or flexed; while projecting ribs or angles, such as an engineer makes in a bar or pillar of iron for the purpose of greatly increasing its strength in the way of resistance to bending, actually make it much weaker than before (for the same amount of metal per unit length) in the way of resistance to torsion.
In the hop itself, and in a very considerable number of other twining and twisting stems, the ribbed or channelled form of the stem is a conspicuous feature. ”

“ A force tending to produce torsion around an axis. An example is the
pulling or turning moment of an armature of an electric motor upon its
shaft. It is often expressed as pounds of pull excited at the end of a
lever arm one foot long.
The expression is due to Prof. James Thompson, then of the University of
Glasgow.
"Just as the Newtonian definition of force is that which produces or
tends to produce motion (along a line) , so torque may be defined as that
which produces or tends to produce torsion (around an axis) . ”

“ KUMASAKA.
Then is all lost. For of these torch-diviners they sing that the first torch is the soul of an army, the second torch is the wheel of Fate, and the third torch—Life itself. All three are out, and there is no hope left for this night’s brigandage. ”

“ The strain produced by torsion or twisting is essentially shear transverse and parallel to the fibres, combined with longitudinal tension and transverse compression. Within the elastic limit the strains increase directly as the distance from the axis of the specimen. The outer elements are subjected to tensile stresses, and as they become twisted tend to compress those near the axis. ”

“ When the fist of a pugilist strikes the body of his antagonist, it sustains as great a shock as it gives; but the fist being more fitted to endure the blow, the injury and pain are inflicted on his opponent. This is not the case, however, when fist meets fist. Then the parts in collision are equally sensitive and vulnerable, and the effect is aggravated by both having approached each other with great force. The effect of the blow is the same as if one fist, being held at rest, were struck by the other with the combined force of both. ”

“ To burst is to break by pressure from within, as a bombshell, but it is used also for the result of violent force otherwise exerted; as, to burst in a door, where the door yields as if to an explosion. To crush is to break by pressure from without, as an egg-shell. To crack is to break without complete severance of parts; a cracked cup or mirror may still hold together. Fracture has a somewhat similar sense. In a fractured limb, the ends of the broken bone may be separated, tho both portions are still retained within the common muscular tissue. ”

“ Thus collisions which might result simply in deflection if the particles acted severally, produce fracture when they act conjointly. Particles may produce pressure when they act separately, but when they act conjointly pressures may lead to rupture. By the device of the lever forces are multiplied in effect without increase or diminution of force as such ”

“ If, on the other hand, he cries, “Mortar!” you will be struck by a regular, not disagreeable hissing, which has no connection in your mind with anything terrible. It comes nearer and with greater rapidity. You see the black ball fall to the ground, and the bomb-shell burst with a metallic cracking. The pieces fly in air, whistling and screeching; stones hit each other, and mud splashes over you. You feel a strange mixture of pleasure and fright at these different sounds. At the instant the projectile reaches you, you invariably think it will kill you. ”

“ The flaring torch he dashed full at a grisly muzzle that snapped and slavered at his legs. To their nostrils the singe of burned hair wafted. Yelping, the beast swerved back.
But others ran in and in at them; and now the torch was failing. Both of them shouted and struck; and the revolver stabbed the night with fire.
Pandemonium rose in the forest. Cries, howls, long wails and snuffing barks blent with the clicking of ivories, the pad-pad-pad of feet, the crackling of the underbrush. ”

“ Fig. 320. Head of Ovis Ammon, shewing St Venant’s curves.
But there is yet another and a very remarkable phenomenon which we may discern in the growth of a horn, when it takes the form of a curve of double curvature, namely, an effect of torsional strain; and this it is which gives rise to the sinuous “lines of growth,” or sinuous boundaries of the separate horny rings, of which we have already spoken. It is not at first sight obvious that a mechanical strain of torsion is necessarily involved in the growth of the horn. ”

“ The torch makes a flame that will cut through two inches of solid steel in less than a minute and pierce a twelve-inch piece of the hardest steel in less than ten minutes—a task that would take a saw almost twenty hours to accomplish.
When the soul burns with the heat of great enthusiasm, it will burn through obstacles that are entirely insuperable to ordinary efforts. ”

“ And, at times of strain, when more pressure is needed, there is no increase in pressure to meet that need.
This unregulated pressure tends to stretch the weakened muscles at the point of rupture—distends and enlarges the opening.
That is one reason why a rupture grows constantly worse when a leg-strap or spring truss is worn. Such trusses are a crime—wearing them is simply slow suicide. ”

“ A hurried altercation in low tones, a subdued word of command, [Pg 64] and a dozen men, their rifles and entrenching tools slung over their shoulders, applied themselves to the back of our car, and slowly it slithered out of the mud. The column broke into file to allow us to pass, my companion went on ahead with a tiny electric torch to show the way, and with infinite caution we nudged slowly along the rank, the faint light of the torch bringing face after face out of the darkness into chiaroscuro, faces young and fresh and ruddy. ”

“ For instance, the line of gravity of the body is, by some cause, removed behind it; the anterior muscles contract themselves to bring it forward again; the extensors act on the rotula; it is broken, and a fall ensues. Again, the leg is suddenly thrown into a state of violent extension; the extensors act with great force; a fracture is the consequence, and the patient falls. A soldier once fractured his rotula in kicking at his serjeant; thus the olecranon, in like manner, has been broken by throwing a stone. ”

“ Strange as it may seem, the brass tip of the torch does not melt in this heat because the pressure behind the gases forces them out with such velocity that the flame is far enough removed from the tip to do it no injury, just so long as the operator does not put the tip square against the metal and drive the flame back against it. ”

“ The causation of concussion is, however, materially influenced in its degree by the velocity of flight of the bullet and consequent severity of the vibratory force exerted. Hence actual contact of the bullet with the nerves is not necessary for its production, as is seen in the temporary complete loss of functional capacity in the limbs in many cases of fracture, where the vibrations are rendered still more far-reaching and effective as the result of their wider distribution from the larger solid resistance afforded by the bone. ”

“ In difficult crack climbing the extent to which pressure, the jamming of a leg, the touch of a calf or knee, or the twisting of a hand or forearm can be used to ease the muscular strain must be learned by practice. A fist or finger may be hooked in a smooth rift, or a foot slanted into a crack, with only friction attachment, and a slight twist to arm or leg converts either into a secure lever for lifting the weight. The clenching of the fist or the tightening of the muscles of a jammed forearm, or even the inflation of the chest, may at need serve the same purpose. ”

“ So, with a little electric torch in one hand and the other held out blindly before me, I crept into the darkness that was, presumably, Vining’s entrance hall.
After a moment I heard the front door close softly behind me, and then I ventured to use the torch.
Have you ever gone into a strange house and tried to make out the lay of the land with a pocket torch? The torch shows up only one tiny spot at a time, and when you have swept it all over one article of furniture and made out its general dimensions, you have forgotten everything else! ”

“ For often, when we are carrying a lighted torch, although we incline its head downwards, we cannot compel the force of the flame to direct itself to the ground; but still it turns upward, and passes from below toward that which is above. ”

“ It is this force, multiplied by the weight of the ball, which gives it the destructive power. If this ball is brought into collision with the foot of a person, such destruction ensues as generally to necessitate amputation. ”

“ The right hand being properly bandaged with a handkerchief, the stone to be broken is taken with the left and allowed to rest upon a larger stone or upon an anvil. Then the stone to be broken is struck with the right fist, while care is taken to raise it a slight distance above the anvil just before the fist touches it. The stone then takes on the velocity of the fist that strikes it, and coming into violent contact with its support, is very promptly broken. ”