II. A new form of spring for electric and other measuring instruments

Abstract

In steam and gas engine indicators, the pressure of the fluid on a piston produces a slight shortening of a spiral spring which is magnified by a lever, and so the pressure of the steam or gas is recorded. In what are usually known as spring balances there is also occasionally a magnification of the elongation of a spiral spring effected by the use of a rack and pinion.. Such magnifying arrangements, however, hot only introduce inaccuracy by the bad fitting of hinges or of teeth, an inaccuracy which is aggravated by wear, but they increase the cost of measuring instruments and their liability to get out of order. And, as an example of the difficulty of using a wheel and pinion for the magnification of an angular motion produced by a small force, we may mention that although we used this plan for a year or more in our electric measuring instruments, and although the wheels and pinions were made by a good watchmaker, still the friction involved in such a plan has induced us to abandon it in favour of the new arrangement which is the subject of this communication.