scope with vacuum thermocouples in full daylight when the planet was near the meridian. Three different thermocouples were used. Couple No. 36, made with octagonal receivers 0.8 mm in diameter, was used most frequently.4 No. 40, made for lunar investigations, was partially covered with a silver shield which exposed only one receiver, 0.45 mm square. No. 42, with receivers 0.2 mm in diameter, which had been made for measures of details on Mars, was also used for some detailed measures on Venus. These thermocouples, each with a mass of about 0.01 mg, had blackened receivers and were used in cells with rock-salt windows, evacuated to pressures lower than those in X-ray tubes. A Leeds and Northrup high-sensitivity galvanometer of 1 -second period was used with 150 ohms in series to reduce the deflections and to increase the speed of registering them photographically.