Drive them forth with such air, in the division G. INCANDESCENT GAS LIGHTING. The hot-water supply--The tank system--The cylinder system--How a lamp works--Gas and gasworks--Automatic stoking--A gas governor--The gas meter--Incandescent gas lighting 386 Chapter XX.--VARIOUS MECHANISMS. CLOCKS AND WATCHES. A SHORT HISTORY OF TIMEPIECES. A clock or watch contains three main elements:--(1) The source of illumination.