GAUGES, STEAM. Bristol's Recording Presmre-Gottge.—This instrument (shown in Figs. 1 and 2) is a recent invention of Prof. W. IL Bristol, of the Stevens Institute of Tech nology. Fig. I represents the instrument complete and ready for application. Fig. 2 shows the pressure-tube with the inking-pointer attached ; the front of ease, dial, and cover of clock being removed. The pressure-tube A is of flattened cross-section, and b'ent into approxi mately a sinusoidal form. A flexible strip B, of the same metal as the tube, is secured at the ends and along the bands, as shown in Fig. 2. The bent tube may be considered as a series of Bourdon springs placed end to end. Pressure applied to the tube produces a tendency to straighten each bend, or collectively to elongate the whole. This tendency to lengthen the tube is resisted by the flexible strip 11, and thereby converted into a multiplied lateral motion.
The inking-pointer is attached directly to the end of the pressure-tube, as shown in Fig. 2. The usual mechanism and multiplying devices are dispensed with, since the motion of the tube itself is positive and of sufficient range. The special advantage of this is evident, con sidering that in all other pressure-ganges the movement of the tube or diaphragm is small, and requires a system of mechanism to multiply the motion many times before it is available for indieating purposes. These multiplying devices, even under the most favorable conditions,
ore liable at any moment to lie a source of error. In the instrument illustrated the tube is designed for a range of 180 lbs. per sq. in.; for other ranges its sensitiveness may lie varied at will. by changing its proportions, as length, shape of cross-section, or thickness. The printed charts for receiving the re e 0 I'd make one revolution in 14 hours, and are provided with radial arcs and concentric circles, the divisions on the radial arcs corresponding to differ ences in pressure, while those on the concentric circles correspond to the hours of the day and night. The in strument is adapted for a vacuum as well as for a pressure-gauge. and, if sufficiently sensitive, it will serve as a barometer, and measure changes of atmospheric pressure. Another ap plication of the pressure-tube is in the reeording thermometer. The tube may he filled with a very expansible liquid. such as alcohol, and sealed. Variations in temperature produce expansion of the inclosed liquid. which in turn give deflections of the tube to correspond.