120 THE ROYAL SOCIETY OF CANADA 
We do not propose in this paper to publish any definitive values 
of the solar rotation, they will be withheld until a series has been ob- 
tained and measured. It may be of interest, however, to present a 
few measures of some of the experimental plates obtained which will 
give an idea of the relative accuracy attainable. 
The measures given in the following table are of plates at 0° latitude 
obtained nearly a year ago, shortly after grating No. 55 was received. 
They were taken in the second order of this grating about the region 
À 4500, which was used before the definite allotment of regions at the 
Solar Union. The linear dispersion here is about 1-02 Angstroms to 
the millimetre, considerably less than used by Adams. However, the 
definition in the 2nd order was so much better than that in the 3rd at 
this region as to more than compensate for the diminished dispersion. 
29 lines were measured on each plate by Plaskett with the result shown 
below. 
MEASURES OF TEST PLATES. 
528 a 531 a 531 b 566 a 566 b 
Disp.| Vel. | Disp.| Vel. | Disp.| Vel. | Disp.| Vel. | Disp.| Vel. 
4432-736. .|-0569 | 1-882 | -0570 | 1-885 | -0573 | 1-895 | -0556 | 1-839 | -0573 | 1-893 
4435-321...) 559) 848 572| 890) 574| 897 557| 840 555| 834 
4438-570..| 569| 880] 573| 892 570| 882 552| 823 563| 859 
4445-641..| 562| 852 559| 843 567 869 548 | 807 557| 836 
4454-552..| 557| 832 565 | 858 563| 852 543 786 556| 829 
4464-617..| 571 873 575| 886 577 | 892 562| 843 553| 814 
4468-663..| 571 870| 564| 848 573| 877 564| 847 567 857 
4484-392..| 578| 882 570| 858 566| 846) 568| 852 570| 858 
4489-911..| 581 892 570 | 857 572| 863 553| 801 565| 841 
4502-388..| 580] 882 576| 869 575| 866 554| 798 553| 795 
4508-455..| 588} 905] 571 850 574| 860) 568| 841 566| 834 
4512-906..| 570| 846| 569; 843 584] 891 573| 855 560! 813 
4518-198..| 585) 890) 580| 874] 586] 894; 566) 830| 572) 849 
4523-572..| 585| 888 597 926 587 894| 576] 858 572| 846 
4527-101..| 571 841 584; 883 584; 876| 565); 822 569; 835 
4531-S01..| 573} 845) 583} 877 581 871 561 806| .558| 796 
4534-903..| 580} 866} 592| 905 584} 879 580] 866; 572) 840 
4546-129..| 579) 857 579| 857 571 832 575| 844) 571 832 
4548-938..| 585) 875 591 894 590| 891 564] 808 574| 840 
4554:211..| 576| 843 582| 862 591 891 572| 830 577| 846 
4555-662..| 574| 837 582| 862 586| 875 571 827 569| 821 
4558-827..| 589| 883 579| 851 576| 841 576| 841 572| 829 
4563-939..| 587| 873 585} 867 575| 835) 567 810 577| S841 
4571-275..| 586| 867 585| 864 575| 832 572| 822 570} 816 
4572-156..| 589} 875 587 869 594] 891 573| 825| 578] 840 
4578-732..| 578} 838 586| 863 591 879 575| 829 570} 812 
4590-126..| 577 829| 576 826 597| 892 580| 838 574| 819 
4602-183..| 597| 886] 589 861 593| 874 564 792 579| 829 
4603-126..| 593| 873 5791 829 582! 839] 576! 820| 571 S04 
Mean velocity... 1-866 1-868 1-872 1-828 1-834 
Probable error 
ner ire TOUL Ee O15 EE O15 + -013 + -015 
Corrected  velo- 
CMNES eon esas 2-055 2-056 2-060 2-012 2-018 
