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March, 1930] WATER COOUNG OF INCANDESCENT LAMPS TRANSMISSION CURVE FOR WATER
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In any consideration of the elimination of heat from a beam of light, one thinks immediately of the water cell. The International Critical Tables (Vol. 5, p. 269) provide data for the transmission of water, and Fig. 3 is plotted for a layer of water 1 cm. thick. As is shown by the curve, the transmission of 1 cm. of water is high for the ultra-violet, and 99 per cent or more through the visible spectrum. At Ifi it falls to 66 per cent. Beyond lju there is one slight rise, but the transmission
V*
/o
V C}=3.67 XT'* WATT C
FIG. 2. Energy distribution curve for a black body at 3500 °K.
then falls rapidly to 30 per cent at 1.24^ and at I AH is only 3 per cent. At 1.5/j the transmission is practically zero. In other words, water is a very suitable absorbent for heat and has an excellent transmission for visible radiation.
EXPERIMENTS ON RELATIVE ABSORPTION OF LIGHT AND HEAT
The preceding paragraphs have indicated that it should be possible to remove much of the heat from an incandescent lamp by means of a water cell a centimeter or two thick with the loss of but very little light. Data will now be presented showing the relative transmission of light and heat in experiments made in the laboratory with not only water, but also copper chloride solutions as the absorbing media. The first experiment measured the per cent of light and heat from a 400 watt projection lamp transmitted through a water cell one centimeter thick between parallel glass plates. The second experiment involved measurements on a 150 watt lamp operating in air within a double