A standard thermograph was adapted to the regulation of variable temp. Three parts were fastened to the thermograph: An electrically insulated platinum or silver contact point replaced the pen, a cylinder of tinned iron roughly plated with chromium was fastened to the clock, and an insulated binding post was clamped to the frame. The electrical system called for a source of direct current and a relay coil having a current drain of 10 to 15 milliamperes at 3 volts. The temp. program was traced on the cylinder. The metal below and adjoining the line was insulated by means of hard-drying automobile lacquer. In operation, the current passes through the thermograph, with the positive lead connected to the platinum point. With a rise in temp. the point makes contact with the chromium and turns off the heat; as the temp, drops, the point falls back onto the lacquer and turns on the heat. As the clock revolves, the point tends to follow the upper margin of the lacquer.