TRANSACTIONS OF SECTION A. 291 
2. Mount Stromlo Observatory. By P. Baraccut. 
The Government of the Commonwealth, wishing to define a spot within the 
Federal Territory the meridian of which should be adopted as the Prime Meri- 
dian of Australia, to serve as the common longitude datum for all State surveys, 
decided to mark the spot by erecting upon it a small astronomical observatory 
which, if the selected site proved to be sufficiently good for the most delicate and 
important class of astronomical observation and research, was to be expanded 
and equipped as a modern observatory of the first order, including a department 
for the study of the sun. 
The site was selected in the year 1910; a concrete structure with an eighteen- 
foot dome was subsequently erected, and a nine-inch refractor by Grubb, equa- 
torially mounted, was installed in September 1911. 
With this instrument astronomical observations, visual, photographic and 
spectroscopic, were carried out during one week of each month in the year 1912 
and till April 1913, after which sufficient evidence was collected to show that the 
site was suitable for a first-class observatory. 
Since then this observatory has remained inoperative pending the decision of 
the Government as to its future. 
In this paper the site of the observatory, the instruments, and the work done 
were briefly described, with the object of placing sufficient information about this 
matter before the British Association to enable it to recommend to the Common- 
wealth Government the general lines on which this observatory should be 
enlarged and equipped, and what should be the programme of its future work. 
3. Proofs of the Sun’s Variability. By C. G. Axssor. 
It has been shown by experiments of the Smithsonian Astrophysical Observa- 
tory conducted simultaneously at Mount Wilson in California and Bassour in 
Algeria, in the years 1911 and 1912, that the values of the intensity of the solar 
radiation outside the atmosphere estimated by spectrobolometric observations at 
the two stations on the same days are, within the limits of error, identical. The 
measurements at the two stations agreed within an average deviation of about 
1 per cent. It appeared, however, that the values of the solar constant of 
radiation obtained deviated over a range of nearly 10 per cent. during the con- 
tinuance of the expeditions. This deviation was observed at both stations, 
so that if high values were obtained in California high values were obtained 
simultaneously in Algeria, and vice versa. Professor Turner has computed, from 
the observations, the coefficient of correlation between the results at the two 
stations. He finds this coefficient to be 52 per cent. plus or minus 7 per 
cent. if all the observations are used. Rejecting three observations of extreme 
doubtfulness, the correlation coefficient rises to 60 per cent. This furnishes very 
strong evidence of the variability of the sun, which appears to be irregular in 
period and irregular in amplitude, but may range over a course of 5 per cent. 
or even more within the lanse of a week. 
Measurements of the solar constant of radiation have been conducted on 
Mount Wilson in California by the Smithsonian Astrophysical Observatory for 
about eight years, though unfortunately the observations have been confined to 
the months of summer and autumn, when the sky is favourable there for them. 
It is highly important that such work should be taken up at another station, or 
preferably at several other stations, where favourable conditions of the sky 
would be found in the other months of the year. 
When the monthly mean values of the solar constant as obtained on Mount 
Wilson are compared with the sun-spot numbers of Wolfer, it is found that 
increased sun-spot numbers correspond with increased values of the solar radia- 
tion and vice versa. Professor Turner has computed the correlation coefficient 
for these two variables as depending upon fifty months of observations, and 
finds this coefficient to be 53 per cent. plus or minus 7 per cent. Here also it is 
seen that a strong proof of the variability of the sun’s radiation exists. It 
appears therefore that the sun, besides varying from day to day in the manner 
shown by the combined Algerian and Mount Wilson observations, also varies 
from year to year in connection with the march of the sun-spot cycle. 
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