268 
PRESTON. 
It is proposed to carry on latitude observations of precision 
at two of these stations for a period of at least five years, 
possibly longer, at the end of which time sufficient data will 
be at hand, when taken in connection with the Japanese and 
Italian work, to predict the position of the pole with much 
greater precision than could be done hitherto. The cost of 
the entire work will be about $10,000 annually, but the In¬ 
ternational Geodetic Association has considered the benefit 
to science commensurate with the outlay, and the project 
will be taken up in the near future. 
In this connection we may remark that, although the 
method just outlined is without doubt the most perfect that 
can be devised where several observatories contribute to the 
result, the same end may be attained by observations in 
two localities. Such a method has been proposed by Pro¬ 
fessor Harkness, and some of the necessary observations are 
now going on at the U. S. Naval Observatory. Making use 
of the fact that two stars, each of the first magnitude, culmi¬ 
nate about the same time and on opposite sides of the zenith, 
he has availed himself of their position and brightness to 
make observations at every meridian passage day and night 
through the entire year. The simplicity and elegance of 
the procedure lies in the fact that an effectual check is 
secured through the invariability of the sum of the zenith 
distances of the two stars, whatever may be the change in 
latitude. The change in the difference of their zenith dis¬ 
tances is, moreover, twice the latitude variation. Since the 
effect of aberration will necessarily have its influence on 
these results, it is proposed to make it the subject of a sepa¬ 
rate determination, utilizing four other stars, when the effect 
has its maximum value. Greater accuracy is therefore se¬ 
cured by observations under the most favorable conditions, 
and the effect of aberration can be successfully eliminated. 
The complete motion of the pole is then obtained by com¬ 
bining the observations on « Lyrae and a Cygni with those 
made at some station 6 hours east of Washington, and thus 
practically the same result will appear from two stations as 
would be furnished by four in the scheme above mentioned. 
