Polished Mirror Research Articles

Photometer for controlling the surface quality of polished technical glass and mirrors

Photometer for controlling the surface quality of polished technical glass and mirrors

AN IMPROVED ELECTRONIC DEW-POINT HYGROMETER

Abstract After a theoretical discussion of the basic physical principles involved in the dew-point method of hygrometry, which serves to establish the inherent advantages of the technique, the paper describes the operating principles and the design of an improved, automatic, electronic dew-point hygrometer for laboratory or field use. The instrument makes use of photoelectric detection of condensation on a cooled, polished metal mirror combined with a radio-frequency induction heating system and an all-electronic proportional heat-control servo system. The instrument makes possible the continuous and automatic measurement of atmospheric water-vapor under all conditions of temperature with nearly constant accuracy and small lag.

The Total Emissivity of Various Materials at 100–500°C

Total emissivities have been obtained for various metal, carbon, paint-coated, and glass samples. The carbon and glass samples were measured at about 500, 320, and 100°C; the others only at 100°C. The equipment consisted of a thermopile, three diaphragms, and three shutters, all at 0°C, and suitable heaters. For calibration, a special blackbody at 100°C was used. Its principal feature was a polished conical brass mirror, also at 100°C, for reflecting blackbody radiation to the thermopile.The emissivity data for glass were corrected for radiation transmitted through the sample from the blackened heater surface, and for the temperature gradient in the sample. The resulting emissivity values ranged from 0.82 to 0.91 for two glass samples and from 0.67 to 0.775 for fused quartz. For pressed carbon plates, the range was 0.71 to 0.77; for radiator paints, 0.29 to 0.84; for well polished metals, 0.05 to 0.135.

III. On the reflection of Röntgen light from polished speculum-metal mirrors

It has been generally supposed th a t the X rays cannot be reflected.Some experiments I have carried out in my laboratory at Blythswood induce me to believe that the X rays can be reflected.