L I 6 R A R 



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THE DOMINION ASTRONOMICAL OBSERVATORY AND 

 THE BOUNDARY AND GEODETIC SURVEYS. 



Astrophysics. 



Visual observations of double stars have formed part of the work 

 with the 15 inch equatorial refractor but as previously the principal 

 work has been the spectroscopic determination of stellar radial veloci- 

 ties with special attention to spectroscopic binaries. During the 

 year ending May 1st, 531 stellar spectograms have been secured and 

 the orbit of one spectroscopic binary determined. Additional work 

 on some previously secured orbits has been carried on which will 

 shortly be published. 



The decrease in the number of spectrograms secured has been 

 due to poor observing weather, much the worst since the Observatory 

 has been opened. This and the decrease in the number of stars 

 available with this telescope will explain the falling off in the number 

 of orbits obtained. 



Experimental work undertaken with a view to increasing the 

 efficiency of the spectrograph has conclusively shown that a consider- 

 able saving in exposure time and consequent increase in output and 

 range results from the use of a prism of lighter glass than the dense 

 flint usually employed and this with other improvements in the 

 optical train easily effects a saving of forty per cent. 



Work on the Solar Rotation with the Coelostat Telescope and 

 Grating Spectrograph has been actively continued. Two series of 

 Rotation Plates one in the special region at X 5600 and the other 

 in the general region at X 4250 have been secured in pursuance of 

 the International scheme adopted. A further series with a new 

 reflecting prism device giving a much greater quantity of observing 

 material and permitting, it is hoped, some new conclusions to be 

 reached has also been obtained. The measures of the 1912 plates 

 show a very close agreement with those of 1911, within one half of 

 one per cent, and the conclusions reached previously have been 

 confirmed. 



The contracts for the 72 inch reflecting telescope were awarded 

 last fall. For the optical parts to the J. A. Brashear Co., Pittsburgh, 

 and for the mounting to the Warner and Swasey Co., Cleveland. 

 The design of the mounting, upon which a great deal of time has been 

 spent, is practically completed and construction work will shortly 

 commence. The work of grinding and figuring the large mirror 

 will begin as soon as the disc is received from the glass makers. 



