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MEETINGS OF THE SOCIETY
December 10, 1918,-The Society held its regular meeting at 8 p.m., the President, Mr. A. F. Miller, in the chair.
A summary of the business transacted at the meeting of the Council on December 6 was announced, viz., that the names of those in arrears beyond a fixed limit had been erased from the membership roll; that owing to the unsatisfactory conditions of the place of meeting, the Council had authorized enquiries to be made for another place; that nominations had been made for officers for 1919 agreeably to the Constitution; that a Committee had been appointed to make arrangements for the Annual AtHome; and that instructions had been given to have the Lists of Members printed.
Professor Satterly mentioned a peculiar haze on the evening of December 4th, and Mr. Miller referred to an aurora, with some streamers, on the night of December 8th, and into the morning of the 9th. Professor Satterly asked if the Handbook, which was reduced in size owing to the war, could be enlarged again, especially for the planet positions, and in reply Professor Chant explained that the maps that had been supplied to members could still be used and would obviate an immediate restoration of the columns of figures, etc.
The decease of Mr. C. Robson, a member of the Society in the army service, was referred to.
Professor J. Satterly gave the paper for the evening on ascer
taining "The Temperature of the Sun" by radiation methods. Radiation he defined as a process of transfer of energy through empty space. When this radiation is absorbed, it is converted into heat. It may be measured by the differential thermometer with two bulbs, one of which is coated with lampblack. The first person to measure radiation in this way was Sir John Leslie, a Scottish scientist. The next important instrument of measurement was the thermopile of Seebeck, who found that an electric current is produced if the junctions of two metals are at different temperatures. This instrument is very sensitive to radiation. The bolometer may also be used. This instrument acts upon the principle that electrical resistance varies with the temperature.
Newton, in 1770, estimated the radiation of the sun, but there was not much further advance in the subject until Stefan, in 1879, tcok up Tyndall's experiments and found the law which Dulong and Petit, as well as Tyndall, had overlooked, or had failed to discover, viz., that the radiation from a hot body is proportional to the fourth power of its absolute temperature. On this principle the effective temperature of the sun is found to be about 6000 degrees Centigrade. A correction for the amount of absorption in our atmosphere has to be made.
Another method is to make a calculation from the area of the - sun's disc, and thereby ascertain that it would take about 200,000 suns to completely fill the sky. From this fact, applying Prevost's theory of exchanges, it is found that the sun's temperature would be about 5,800 degrees Centigrade. The temperature at the surfaces of Mars and Venus could also be measured by this method.
Finally, by the spectrum curve method of calculation, its temperature is found to be 5,900 degrees.
A fuller account of the paper appears on page 33 in this issue.
THE DOMINION ASTROPHYSICAL OBSERVATORY
SECOND LIST OF SPECTROSCOPIC BINARIES
The following table contains a list of 18 binaries discovered in the course of the radial velocity work of this observatory. The first list of 12 binaries was published in the November, 1918, issue of this JOURNAL, which, with this list, makes 30 to date.
As in the first list, the serial numbers are continued and the binaries are arranged in order of right ascension for convenience of reference. Notes in regard to the character of the spectrum and other remarks which are too long to be incorporated in the table, are given below the latter, the purpose being to make the data about each sufficiently complete to enable observers desiring to work at any of these binaries to decide on the character of the spectrum and its suitability for obtaining an orbit without making test plates.
In the table, column 1 gives the serial number of the binary. Column 2 gives the number of the star in Boss's Catalogue and in the Revised Harvard Photometry and its Right Ascension and Declination for 1900. Column 3 gives the visual magnitude and spectral type from the Henry Draper Catalogue, the unpublished data being kindly supplied by Prof. Pickering. Column 4 gives the date of the observation of each plate. In column 5 in this list is given the Julian day and fraction of a day of the observation in preference to the Greenwich mean time in hours and minutes, as in the previous list. Column 6 gives the measured radial velocity to tenths of a kilometre. Column 7 gives the respective quality of the individual plates as regards suitable exposure and development, but does not give any indication of the character of the lines, which is discussed in the supplementary remarks. The last column gives the discoverer, P standing for Plaskett, Y for Young.