IN this paper experiments are described showing that there is but little difference in the radiation sensitivity of stellar thermocouples constructed of bismuth-platinum, and thermocouples of bismuth-bismuth + tin alloy, which have a 5 ยฐ per cent. higher thermo-electric power.
Improvements are described in the method of maintaining a vacuum, by means of metallic calcium, whereby it will be possible to go to the remotest stations for making radiation measurements without carrying an expensive vacuum pump.
With this outfit measurements were made on the radiation from II2 celestial objects, including lO 5 stars. This includes measurements on the bright and the dark bands of Jupiter (also a pair of his satellites), the rings of Saturn, and a planetary nebula.
Quantitative measurements were made on stars down to the 5.3 magnitude, and high-grade qualitative measurements were made on stars down to the 6.7 magnitude.
it was found that red stars emit from two to three times as much total radiation as blue stars of the same photometric magnitude.
Measurements were made on the transmission of the radiations from stars and planets through an absorption cell of water. By this means it was shown that, of the total radiation emitted, the blue stars have about two times as much radiation as the yellow stars, and about three times as nmch radiation as the red stars, in the spectral region to which the eye is sensitive.
A stellar thermocouple and a bolometer were compared, and the former was found to be more sensitive. The conclusion arrived at is that, from the appearance of the data at hand, * Communicated by the Bureau.