MOTION OF THE SOLAR SYSTEM. 
93 
sion and declination was first deduced from the comparison of each catalogue with 
Lacaille’s places, and the mean of the two comparisons then taken and made use of 
in the subsequent calculations. 
Having thus obtained the places of the stars for the mean epoch 1790, and the 
annual variations in right ascension and declination being found by dividing the 
differences of the catalogues (expressed in seconds of arc) by the number of years in 
the interval, the angle which the apparent path of the star makes with the circle 
of declination, was computed. This angle determines the position of the great circle 
of the sphere in which the apparent motion takes place. 
The next step in the process is to compute the angle %//, or the direction in which 
the star would appear to move in consequence of the translation of the sun towards 
an assumed point Q. With respect to this point, or apex, the position which may be 
regarded as the most probable is, perhaps, that which was deduced by Otto Struve 
from the five determinations above given ; but the object here was not to choose the 
point which has the greatest probability in its favour, but that which appeared the 
most likely to satisfy the present observations. Now, on examining the apparent 
motions of the stars under consideration, it was easy to see that the apex must have 
a considerably greater declination than that which was assigned to it by Lundahl. 
Otto Struve’s result, on the other hand, which differs from the mean in the opposite 
direction, appeared to me to be less trustworthy from the manner in which it was 
deduced. I therefore assumed, as the apex of the solar motion, the point determined 
by Argelander, though, as it turns out, the motions in declination would have been 
somewhat better satisfied by assuming the mean of all the results as given by Otto 
Struve. Its position for 1790 (the mean epoch of the catalogues) is 
A = 259° 46 , ’2, D=-f 32° 29'-6*. 
From these values of A and D the angle -p' was computed for each of the eighty-one 
stars separately. The results, as well as the values of -p, and the differences p—p', 
will be found in a table hereto subjoined. 
Before proceeding to state the results obtained from the equations of condition, 
it will be worth while to examine the presumptions for or against the hypothesis 
deducible from the comparison of the directions of the apparent proper motions of 
the different stars, and the directions of the parallactic motions which would result 
from the motion of the sun towards the assumed point Q. 
First, with respect to the observed variations of right ascension : if we conceive the 
celestial sphere to be divided into two hemispheres by a great circle passing through 
* This is the position according to the values of the right ascension and declination given by Argelander 
in No. 363 of the Astronomische Nachrichten, but in a subsequent number of the same work (No. 398) it is 
stated that an error of calculation had been committed the correction of which would have given the position 
of Q, for 1792*5 as follows : At=260° 51', Dec. = + 31° 17'. The correction was not observed till after the 
values of had been calculated for all the stars ; but for the present purpose the difference is manifestly of no 
importance. 
