ASSMANN PSYCHROMETERS

The bulb of one of the thermometers is covered with thin muslin which is moistened with distilled water before use . The thermometers are suspended in the frame with their bulbs surrounded by two thin coaxial metal tubes which are chromium plated and highly polished , they are thermally insulated from the rest of the frame by retaining pieces and protect the bulbs from the effects of exposure of solar radiation . The tubes may be removed from the frame by unscrewing the retaining pieces. Ventilation of the bulbs is provided by the fan driven by the clock work mechanism encased in the housing at the top,air being drawn past the bulbs and up the hollow central column.