=Brearley’s Curve Tracer.=—This apparatus made by the Cambridge and Paul Instrument Company, is designed to take a large-scale record of an operation which only occupies a short period of time. It consists of a drum, round which the record paper is wound, and capable of rotating on its axis once in ten or thirty minutes by the aid of clockwork. Attached to the arm of the pen is a pointer, which moves along the scale of a sensitive mirror galvanometer to which a thermocouple is connected. The operator, by turning a handle, moves the drum longitudinally so as to keep the pointer opposite the centre of the spot of light, and this movement is traced on the chart, combined with the rotary movement, by the pen. In this manner the large change in deflection, due to a few degrees increase or decrease in temperature, can be recorded in ink. This instrument is of special service in recording the critical points of steel, or any operation which involves delicate readings over a limited range of temperature. Index Air pyrometers, 219. Anti-vibration stand for galvanometers, 47. Atmospheric temperatures, measurement of, 96, 132. Automatic compensators, 66. _Barrett, Sir W._, discovery of recalescence, 4. _Becquerel, Ed._, optical pyrometer, 5. Black-body radiations, 136. _Brearley_, sentinel pyrometers, 208. — curve-tracer, 221. _Bristol_, air-recording pyrometer, 219. — compensator, 66. _Byström_, calorimetric pyrometer, 201. Calorimetric or “water” pyrometers, 195. — — — special uses of, 203. Centigrade scale of temperatures, 6. Clay-contraction pyrometers, 211. Colour-extinction pyrometers, 189. Colour, in relation to temperature, 167. Comparison of gas and platinum scales, 111. Compensators for cold junctions, 66. Conduction pyrometers, 218. Constant temperature cold junction, 71. Contact-pen recorders, 88. “Critical” points of steel, 94. _Daniell_, expansion pyrometers, 2, 214. _Darling_, automatic compensator, 68. — and _Grace_, liquid element thermocouples, 43. _Day_, extension of gas scale, 15. Electromotive force (E.M.F.) developed by junctions, 31. — — measurement of, 62. Expansion pyrometers, 214. _Fahrenheit_, temperature scale, 7. _Féry_, lens pyrometer, 142. — mirror pyrometer, 143. — optical pyrometer, 174. — spiral pyrometer, 150. Fixed points for calibration of pyrometers, 16, 17. _Foster_, base-metal pyrometer, 39. — fixed-focus pyrometer, 152. — recorder, 82. Furnace, electric tube, 95. — temperatures, control of, by pyrometers, 87. Fusible metals, 209. — pastes, 210. Fusion pyrometers, 204. Gas pyrometers, 219. — scale of temperatures, 11. — thermometer, constant volume, 11.