Lateral pressure

“ The corset reverses this. The constriction binds closest the broadest part; the viscera are displaced downward; the lower umbilical region swells out; the greatest area must grow small, and the smallest enlarge.
The point of greatest pressure, we have seen, was over the cartilages. On both sides the liver will be pressed upon, and this at a point where it is covered by lung only during deep inspiration (Fig. 12) . The lateral pressure will crowd liver and spleen toward the median line. ”

“ In a machine of which each piece is to move with a uniform velocity, if the effort and the resistance be constant, the weight of each piece must be balanced on its axis, so that it may produce lateral pressure only, and not act as a reciprocating force. ”

“ If this material is under water, and is so soft as to be considered semi-aqueous, the pressure per square foot will increase in diminishing proportion to the depth, and the pressure per area will soon approach and become a constant, due to the resistance offered by the lateral arching of the solid material ”

“ Firm pressure on the end of the great toe or tip of thumb will control the entire first zone. Firm pressure on the tips of the fingers or toes control individual zones. Lateral or side pressure on thumbs and fingers or toes will affect lateral or side boundaries of the zones pressed, and also transverse extensions to nostrils, lips and ears. ”

“ If, then, the vertical depth of the earthy particles or sand above the bottom is so small that the arching effect against the sides is negligible, the full weight of the particles in contact, directly or vicariously, with the bottom acts as pressure on the bottom, while the full pressure of the water acts through the voids or on them, or is transmitted through material in contact with the bottom. ”

“ To which comes the answer that, when the thoracic cavity is enlarged, the contained air, partially relieved from pressure, expands, and so loses some of its resisting power; that hence it opposes to the pressure of the external air a less pressure; and that as air, like every other fluid, presses equally in all directions, motion must result along any line in which the resistance is less than elsewhere ”

“ If we stretch a tape upon a flat table, whatever be the tension of the tape it obviously exercises no pressure upon the table below. But if we stretch it over a curved surface, a cylinder for instance, it does exercise a downward pressure; and the more curved the surface the greater is this pressure, that is to say the greater is this share of the entire force of tension which is resolved in the downward direction. In math­e­mat­i­cal language, the pressure (p) varies directly as the tension (T) , and inversely as the radius of curvature (R) : that is to say, p = T ⁄ R, per unit of surface. ”

“ But the pressure is not the same. For, the line a g is the direction in which the pressure of the curve acts at the point g, and the line p q, is the length of the lever-arm on which that pressure acts, to turn [95] the generating circle on its axis (now supposed to be fixt;) but, as the turning force or rotatory effort of the wheels, is by hypothesis uniform, the pressure at g must be inversely as p q; that is, inversely as the cosine of half the angle of rotation of the generating circle; hence it would be infinite at s, the summit of the curve, when this circle has made a semi-revolution. ”

“ Thus, the weight of each separate piece in a machine is treated as acting wholly at its centre of gravity, and each pressure applied to it as acting at a point called the centre of pressure of the surface to which the pressure is really applied. ”

“ The resultant of the internal pressure and the surface-tension is equivalent to a tension along the axis, and the numerical value of this tension is equal to the force due to the action of this pressure on a circle whose diameter is equal to the conjugate axis of the ellipse.
2. When the conic is a parabola the meridian line is a catenary (fig. 11) ; the internal pressure is equal to the external pressure, and the tension along the axis is equal to where is the distance of the vertex from the focus. ”

“ The downward pressure forces the diaphragm up into the chest cavity, decreasing the air space and forcing the water out of the lungs. When the pressure is relaxed the diaphragm goes back into place and the air rushes in. ”

“ In the first place, muscular action may cause the table to turn, but it cannot lift it. As a matter of fact, the ten operators have one hundred fingers applied to its surface. Now, the vertical, or quasi-vertical, pressure of each finger cannot exceed twelve ounces on the average, the chain being composed as it is. They only develop, then, a total pressure of 66 pounds, which is quite insufficient to produce levitation. ”

“ Ascending and Descending Motion. —The rear of the vertically-impelled body becomes vacated of minus-pressure matter, and replaced with medium of space; by the latter, and general pressure, the body is forced upwards as a cork by water. While ascending, the rear is acquiring electric matter and losing the impelling medium,—the velocity of course declines; and when at the highest, the body is at rest in the air for an instant, then is precipitated to the ground. ”

“ In the case of wind pressure on a sloping roof surface, R is the horizontal and L the vertical component of the normal pressure.
In experiments with the whirling machine it is the resistance to motion, R, which is directly measured. Let P be the pressure on a plane moved normally through a fluid. ”

“ Each pulse, therefore, by distending the whole limb and each individual muscle, will press out a little of the fluid contained in the fasciae in the same way as the contractions of the muscles themselves; and it seems to us probable that it is the aid which is afforded to this process, by the gentle pressure exerted on the outside of the legs by a seat which supports them along their whole extent, that renders such a seat so peculiarly restful and agreeable. ”

“ But when either voluntarily or automatically the nerve currents that cause contraction of the muscles of expansion cease, the elastic structures of the lungs and thorax, including the muscles, recoil, the diaphragm ascends, and the ribs by the force of gravity tend to fall into the position of rest. During expansion of the chest a negative pressure is established in the air passages and air flows into them from without. In contraction of the chest there is a positive pressure in the air passages, and air is expelled ”

“ Connected with the cushion is a pressure gauge, and a tube with a cock, for charging the cushion with air from the lungs. Experience shows what pressure is necessary with any given paper, and the gauge enables one to know that the pressure is neither deficient nor in excess of that which is safe for the glass. ”

“ Centre of percussion, the point in which the direction of a blow, given to a body, intersects the plane in which the fixed axis and the centre of inertia lie, making the body begin to rotate about a fixed axis, without causing any pressure on the axis; Centre of pressure, the point at which the direction of a single force, which is equivalent to the fluid pressure on the plane surface, meets the surface. ”

“ In a plane the pressure is always perpendicular to the surface, and the ratio of lift to drift is therefore the same as that of the cosine to the sine of the angle of incidence. But in curved surfaces a very remarkable situation is found. The pressure, instead of being uniformly normal to the chord of the arc, is usually inclined considerably in front of the perpendicular. The result is that the lift is greater and the drift less than if the pressure were normal. ”

“ This theory shows that, when pressure is applied at a point of the edge of a plate in any direction in the plane of the plate, the stress developed in the plate consists exclusively of radial pressure across any circle having the point of pressure as centre, and the magnitude of this pressure is the same at all points of any circle which touches the edge at the point of pressure, and its amount at any point is inversely proportional to the radius of this circle. ”

“ The explanation is found in the uniform distribution of the pressure, the influence of which is thus counteracted, and by the fact that the tissues themselves contain everywhere a certain amount of air at the same pressure. The familiar experiment of holding the hand over an exhausted glass cylinder—which experiment is indeed but a modification of the use of the cupping glass above referred to—illustrates very forcibly the insupportable difficulties which the human body would encounter were not its entire surface uniformly subjected to the atmospheric pressure. ”

“ A Appearance goes for nothing; a large bust and wide hips or shoulders give an impression of slenderness in the waist which may be entirely deceitful.
The total pressure exerted by a given corset is obtained as follows: The areas of like pressures are chalked out on the corset by shifting the bag about under the corset, and testing at every move with the manometer. Knowing the number of square inches in an area and the number of pounds of pressure to the square inch, the pressure exerted on that area is found; adding the pressures in the various areas together gives us a total. ”

“ But the pain usually becomes more violent the instant the compression is removed. For the mere elasticity of the parts alters their figure, i.e. produces internal motions, with an increase of vibrations. Pressure may also increase vibrations in the internal parts, contiguous to those where it checks them ”

“ Aëronauts have never ascended much higher than 7 miles; at that height the barometer stands at 7 inches instead of at 30 inches, and the internal pressure in cells and tissues is not balanced by an equal external pressure. The unequalized internal pressure forces the blood to the surface of the body and causes rupture of blood vessels and other physical difficulties. ”

“ Pneumatics relates to the equilibrium or movements of aërial fluids under all circumstances of pressure, density, and elasticity. The weight of the air, and its pressure on all the bodies on the earth’s surface, were quite unknown to the ancients, and only first perceived by Galileo, on the occasion of a sucking-pump refusing to draw water above a certain height. ”

“ Pressure for Forced Fits.—The pressure required for assembling cylindrical parts depends not only upon the allowance for the fit, but also upon the area of the fitted surfaces, the pressure increasing in proportion to the distance that the inner member is forced in. ”

“ For this Elastical power, according to the Experiment, has no less force of pressure then an hundred pound weight or more: which pressure (as in all flexible bodies that have a Spring power in them) is perpetual and every where in the Aire, if it be there at all. And therefore any Cylinder of Aire in the same height from the ground, and of the same diameter with that of the Sucker of the Pump, will press as forcibly as an hundred pound weight. ”

“ If the body revolve round any axis through the centre of gravity, which is not a principal axis, the centrifugal pressure is represented by two forces, which are equal and parallel, but which act in opposite directions on different points of the axis. The effect of these forces is to produce a strain upon the axis, and give the body a tendency to move round another axis at right angles to the former. ”

“ It presses with a weight of about fifteen pounds per square inch of surface, and its pressure is exerted in all directions, upward as well as downward. An ordinary man sustains a pressure of over one ton on each square foot of his surface, but as the air penetrates all portions of his body and exercises a pressure outward as well as inward he feels no inconvenience. If his body could be so tightly sealed that no air could enter and if then the air of the interior should be removed with a pump, his body instantly would be crushed to a shapeless pulp. ”

“ Friction and pressure changed their lines of incidence with the increasing tendency of man to assume the upright posture, for the surfaces exposed to pressure and friction were only affected when the extensor surface or back of the forearm rested on some supporting object, an attitude extremely common in man as we know him now. ”

“ Again, if the pressure is so uniform as not to be felt, as when the body is immersed in water (paradoxical as this may seem, it is the case that the sensation of Contact is felt only at the limit of the fluid) , we experience the sensation of being in contact with a fluid. (6) Lastly, it would appear that touch is always the result of variation of pressure. No portion of the body when touching anything can be regarded as absolutely motionless, and the slight oscillations of the sensory surface, and in many cases of the body touched, produce those variations of pressure on which touch depends. ”

“ It cannot be accounted for entirely by the friction, as the removal of the paper allows the sand to drop in a mass. The explanation is that the pressure is transmitted laterally to the sides, and as the friction is directly proportional to the pressure, the load or effect of the blow is carried by the proportional increase in the friction, and any diaphragm which will carry the direct bottom load will not have its stresses largely increased by any greater loading on top. ”