Survey of Northeast Greenland. 109 
The smallest interval between two succeeding transits is here 
about 7™. A smaller interval than 5" ought to be avoided under 
the difficult arctic conditions. It further appears that the stars have 
been selected on the principle that two and two make pairs with 
nearly the same zenith distance. In this manner the collimation 
constant is prevented from exercising any noticeable influence. 
It will generally be sufficient to carry on the preliminary com- 
putation for the first and the last star of a group; for the transit of 
the interjacent stars the azimuth of Polaris and the hour angles of 
the equatorial stars may be estimated. As an example I shall here 
perform the preliminary computation for the former of the two above- 
mentioned groups. 
The approximated correction of the sidereal clock 57203 is du 
= — 1h19m,6. — The right ascension of Polaris is a = 17267495 its 
declination 0’ = 88°48'38”. As the first approximation we may 
consider the sidereal time for the transit of an equatorial star as 
equal to its right ascension. The corresponding values for the hour 
angle of Polaris then become: 
for 7 Pegasi, t, — 22h38m38s + 182671495 — about 218127, 
for x Piscium, Ё, = 238221093 = 1526™49s — about 21/55". 
With these values as an argument the azimuth of Polaris is 
taken from the tables corresponding to the above-mentioned formula 
90° — 9” i ; i a 
a А 99° — 3” which makes а„' = + 222'’.9, an = + 174,6. 
70 
4 sin (g — Ô) 
DÉC CT 
For the hour angles of the equatorial star we have {— a 
where the factor =. is taken from the above-mentioned table 
corresponding to the arguments 0, = 29°.7 and д. = 0°.7. In this 
manner we arrive at 
Е — 1 12529: ава в, — | 11™175 
The clock times for the transit of у Pegasi and x Piscium would 
consequently be: 
U, = + 22838138 + 12™29s = 1519™.6 — about 21531™.5 and 
U, = - 2362202098 —- 111173 = 1519™.6 — about 22513™.8. 
If we compare the moments of transit calculated a priori with 
the result of the observations quoted below, it will appear that the 
transit moments observed (the mean of all the threads) are 21530™.9 
and 228131.3 respectively. The supposed clock correction du — 
+ 1519™.6 is the right one, and the deviations are simply due to the 
