(551) 
tions of azimuth with the elements of the yearly motion of the pole. 
As with regard to the 14-monthly motion of the pole there is 
no reason to expect changes of the same period in the directions 
of the marks, I have attributed the variation of azimuth to the me- 
ridian direction, and therefore to the motion of the pole only, and 
from the latter I have calculated, assuming a period of 430°/3 days, 
the amplitude and epoch of the above-mentioned part of the motion 
of the pole. 
5. About the reduction of the observations I will communicate 
as much as is required to understand the deduction of the numbers 
to be given below, and also their meaning with respect to the 
14-monthly motion of the pole. The observed time of transit reduced 
to the middle thread, has been corrected for the inclination of the 
axis of rotation, the collimation constant, the clock-correction, and 
also partly for the azimuth of the telescope and the personal equa- 
tion of the observer. 
The azimuth constant of the transit instrument used for this reduct- 
ion is deduced from approximate values of the azimuth of the 
north mark up to 1884, further for the mean azimuth of both marks, 
which approximate values are derived from the results of preliminary 
calculations and are taken so as to vary with the time as regularly 
as possible. A few corrections have been applied to these values: 
10. In agreement with the idea mentioned above, half the differ- 
ence in azimuth of the north and south marks has been added to 
the azimuth of the north mark before 1884. 
2°, periodical corrections have been applied to the azimuths over 
the whole period, which corrections result from a 14-monthly 
motion of the pole according to Dr. HK. IF. v. D. SANDE BAKHUYZEN, 
and are expressed by the formula: 
0.159 ? ¢—2408568 
i= Bl Saeco sce sin (22 —__. ---— i) 
15 430.66 
B and 4 being the latitude and longitude (West of Greenwich) 
of the Leiden observatory. (Proc. Vol. I, p. 202). 
By applying the correction 2 for the periodic motion of the pole 
to the approximate values of the azimuth constant, the corrections 
of that constant deduced from the discussion of the whole series 
of observations are freed from the greater part of the influence of 
the 14-monthly periodic motion as proved by the results. By 
means of the azimuth-differences between the telescope and the 
north mark (before 1884) or the mean of the two marks (after 1884) 
