168 I. P. Косн. 
If we put dr — 0.001, dx becomes — 0.007. 
The error of the determinations of 7 must generally be supposed 
to exceed 0.001 degrees and will even in unfavorable cases now and 
then exceed 0.01 degrees. The little examination shows that when 
computing the single values of x one can scarcely rely upon the 
second decimal; the third decimal can in any case only be con- 
sidered as approximate. 
Before passing on to a comparison between the values of К and 
x I shall premise a few remarks about the value of a comparison 
of this kind. É 
Towards the end of August 1907 a further examination of the 
levellings made till then at the cairns V, IX, X and at the “Skerry” 
showed that the observations, particularly on certain days, presented 
very marked irregularities, which appeared as purely spontaneous 
changes in the correction of the zenith point. That the zenith 
distances were subject to rapid and great variations, experience had 
tought us iong before; the very marked apparent and quite tempo- 
rary changes in the correction of the zenith point were therefore 
looked upon as an indication that the zenith distance had under- 
gone a corresponding change in the period between the two pointings 
“telescope right” and “telescope left”. In order to investigate this 
more closely we resolved that the observer after the pointing of the 
object should immediately read the level of the vertical circle; after 
that the microscopes and then again the level. Finally the direction 
of the telescope was to be controlled, before the instrument was 
reversed or a new object pointed. In this manner we guarded our- 
selves against a possible alteration of the zenith distance expressing 
some sudden change in the adjustment of the instrument. It now 
turned out that the zenith distance was often perceptibly altered 
during the short duration of the reading of level and microscopes. 
On a few occasions we also saw the object shooting quite suddenly 
above the middle horizontal thread or sinking below it. The change 
in the zenith distance might be purely temporary and last for a few 
seconds, but it might also extend over several minutes or a longer 
period. This kind of change in the zenith distance we called “verti- 
cal movement”, and in the observation journal we indicated its 
intensity according to an estimate, 0, 1, 2, and 3, where 0 meant 
that the observation of the object with each test had proved un- 
changed, whereas 3 indicated the highest intensity of “vertical move- 
ment”. It is an obvious fact that this estimate must be rather un- 
certain. The “vertical movement” is tantamount to a change in the 
refraction angle!) and is proportional to the distance. A rough 
!) The angle between the sight line and the straight line between telescope and object. 
