Three methods are known by which a liquid may be subjected to a bodily tension. (1)
The method of the inverted barometer
, familiar to most physicists, by which, with care, a mercury column of many times the barometric height may be supported by its adhesion to the top of the tube. In such a column the hydrostatic pressure is negative above the barometric height, or the liquid above this level is in a state of tension. This tension increases with the height and is propagated in all directions to the walls of the tube. When the upper part of the tube is made elliptical in cross-section and of thin glass, its yielding to the inward pull may be easily observed. (2)
The centrifugal method
, devised by Professor Osborne Reynolds, in which a U-tube, ABCD, of glass, closed at both ends, contains air-free liquid, ABC, and vapour, CD. This tube is fixed to a suitable board and whirled about an axis, O, a little beyond the end, A, and perpendicular to the plane of the board. If CE (see figure) be the arc of a circle described about O, then while rotation continues the liquid between E and A is in a state of tension, increasing from zero (if we ignore the vapour-pressure) at E to a maximum at A. By this method Professor Osborne Reynolds has subjected water to a tension of about 5 atmospheres or 72·5 pounds per square inch, while the author, experimenting in the Cavendish Laboratory in 1886, succeeded in reaching, with alcohol, a tension of 7·9 atmospheres or 116 pounds per square inch, and, with strong sulphuric acid, 11·8 atmospheres or 173 pounds per square inch.
Determination of elastic parameters of grain with oedometric and acoustic methods
