Page:Popular Science Monthly Volume 86.djvu/446

442 a planet. One of the most interesting series of measurements was made on the light reflected from the bright and the dark bands of Jupiter. Both gave practically the same transmission through the water cell, showing that whatever may be the cause of these dark bands, the diminution in brightness is quite non-selective as regards the infrared. Interesting measurements were made on Saturn and its rings. Measurements on a planetary nebula showed no positive indications of radiations from it. However, from the observations on blue and red stars, it was not expected that definite indications would be obtained of radiations from a nebula.

In marked contrast with Venus, Jupiter and Saturn, only about 15 per cent, of the light reflected from the Moon is transmitted by the water cell. This is attributable to the fact that the Moon having no atmosphere, the surface becomes warm from exposure to the Sun's rays, and in turn radiates heat waves, which are not transmitted by the absorption cell of water.

In view of the fact that, heretofore, observers were glad to obtain any indication of the radiation from stars and planets, it is of interest to record that in observing the radiation from Venus it was necessary to place a resistance of 50 ohms in series with the galvanometer in order to reduce the sensitivity and thus keep the galvanometer deflection (which amounted to 127 cm.) upon the scale.

It is of interest to obtain a rough estimate of the total amount of heat received from a star as compared with the heat received from the sun, which is of the order of 1.9 gram calories per square centimeter per minute. This was accomplished by standardizing the thermocouples and galvanometer in terms of radiant power. In this way it was determined that the amount of starlight which caused a deflection of 1 mm. = 34 X 10−14 gram calorie per sq. cm. per minute. Or it would take 100,000,000,000,000/34 minutes, i. e., six million years to raise the temperature of 1 gram of water 1° C. The star Polaris is an excellent example. It produced a galvanometer deflection of 6 mm. Hence it would require only one sixth as long to raise the temperature of 1 gram of water 1° C. In other words, assuming that, in the meantime, all the incoming radiations are absorbed and that no heat is lost by conduction, convection or radiation, then it will require the radiations from Polaris to fall upon 1 square centimeter continuously for one million years in order to raise the temperature of 1 gram of water 1° C. In marked contrast with this value, the radiation from the sun which is transmitted by our atmosphere and falls upon an area of 1 sq. cm. of the earth's surface is sufficient to raise the temperature of 1 gram of water 1° C. in about one minute. Moreover, the total radiation