SECTION III, 1912 [23] Trans. B.S. C. 
The Solar Rotation. 
By J. S. Puasxert, B.A., F.R.S.C., and R. E. DeLury, M.A., Ph.D. 
(Read May 16, 1912) 
GENERAL. 
1. A paper published by the authors in last year’s Transactions 
bearing a similar title gave a brief historical summary of the previous 
work in the determination of the Solar Rotation by the Doppler dis- 
placement of the spectral lines at opposite limbs of the sun. It de- 
scribed the instruments and methods employed in obtaining the spectra, 
the difficulties encountered, and the precautions required for accurate 
work. It also gave some preliminary measures of the velocity at the 
solar equator, but refrained from discussing, except very slightly, these 
results. The present paper contains the results of the measures of the 
three series of rotation plates made during the year 1911, and a discus- 
sion of the various points of interest and value arising from these results. 
It has not been thought necessary to again describe the instruments 
and methods as reference can be made to the previous paper.* It may, 
however, be well to state here that, although the determination of the 
rotation of the sun by the spectrographic method was, as early as 
1905, planned as one of the investigations to be undertaken at the 
Dominion Observatory, delays in the construction of the shelter for 
the coelestat telescope and especially the long delay in obtaining a 
suitable grating prevented much work being done until last year. 
2. The whole plan was placed upon a much more definite basis 
at the Mount Wilson meeting of the International Union for Co-operation 
in Solar Research in 1910, where the regions of spectrum to be investi- 
gated were allotted to the different members of the Rotation Committee, 
a general region to be observed by all was selected (centre at 4250) 
and the various questions to be determined were laid down. It may 
be useful to summarize here the principal points. 
(A) The region to be observed at. the Dominion Observatory is in 
the yellow green, 45500—A5700. 
(B) The general region to be observed by all is from 44220 to 
4280 in the violet. 


* Transactions Royal Society of Canada, 1911, Sec. III, p. 107. 
