Improvements in or relating to Barometers.

摘要

12,326. Darwin, H., and Cambridge Scientific Instrument Co. May 22. Barometers.-With the object of obtaining a rapid and accurate reading of the height of a barometer column, the gauge piece D, the edge of which is brought to the top of the mercury, carries a rack E which gears with a pinion F, means being provided for indicating the motion of the pinion. To secure accuracy of working, the rack is provided with diagonal teeth, and, in order to prevent relative sideways motion of the rack and the pinion, the rack is provided with bearing-surfaces E1 the normals to which meet on the line through the centre of the axis of the pinion at right-angles to this axis and parallel to the plane of the rack; any sideways motion of the rack therefore results in rotation about this line. The pinion is free to rotate about the same line, and is consequently carried round with the rack, with the result that relative side motion does not occur. The pinion is allowed this motion by forming at its centre a circumferential groove F', in which works a circular knife-edge bearing H1 formed in a circular piece H attached to stiff springs J1, on the upper of which presses a grub screw K1, so that adjustment of this screw alters the pressure of the knife-edge bearing on the pinion. The pinion is prolonged to pass freely through holes G6 in a guide G, and to one end is attached a graduated dial O which is viewed through a hole P2 in a casing P, a strip Q having a fixed fiducial line being fixed to this casing. The reading on this dial gives the fractional parts of the usual scale on the tube B surrounding the barometer, the diameter of the pinion being preferably arranged so that one complete turn of the dial 0 corresponds to one of the small divisions on the main scale. In order to keep the ratio of the area of the mercury in the trough to that of the mercury in the tube constant for different instruments, the bottom of the mercury tube A is provided with a sleeve S of adjustable area dipping into the trough U. The preservation of this constancy enables the same scale to be used for different instruments.