Survey of Northeast Greenland. 273 
° It thus follows that determinations of time ought to be performed 
as near to the prime vertical as possible, which demand, however, 
is not an easy one to meet in practice, where travelling and weather 
conditions often place obstacles in our way. Where the determina- 
tion of time is only intended as a support for the determinations of 
latitude or azimuth, or to check the longitude, one may generally 
put up with a comparatively big uncertainty in the clock time; but 
if, on the other hand, the longitude is to be determined by the 
chronometer, one must take care to create the best possible condi- 
tions for the determinations of time. 
As the watches used as chronometers ought not to be taken out 
more often or for longer periods than strictly necessary, a clock 
comparison between the chronometer and the observation watch will, 
as a rule, be necessary immediately before or after the observation. 
At determinations of time it is very desirable to have an assi- 
stant to observe the watch and for recording purposes, but one may 
on an emergency do without him, in a similar manner as in the 
case of the latitude. 
At observations of the sun one ought as a rule to observe the 
limb which eludes the thread, in other words, in the morning the 
lower limb, in the evening the upper. One then points slightly 
within the orbit of the sun (see Fig. 38; the arrow in- 
dicates the direction of the apparent movement of the ae 
sun) and waits for the moment, when the sun eludes 
the horizontal thread. As in this manner one can follow 
the movement of the sun across the threads, one gets 
the moment of taction with great sharpness, even in 
high arctic regions, where the day circle only inclines a few degrees 
towards the horizon. 
Fig. 38. 
Kap Bridgman, 15/V 1907. Afternoon. Determination 
of time. Observer: Koch; Assistant: BERTELSEN. ©; b = 769 mm; 
= + 10°.5; g = 83°29'17”; 1 division of the level = 20”; approximate 
clock correction to Grw. $ = about + 1530™. Instrument placed on 
glare ice, in the immediate vicinity of the coast. 
Telescope left 
Telescope right 
| 
| || | | ; 4 Il 
| Vernier | Level | | Vernier | Level 
| 
| 
Clock time |- -— ке | 
ГА В. | Obs. FODE | A | B [0% Obi. 
РЕ Fe и. 
6h29m14s | 288039.7 | 404 | 11.6 | 5.9 | 6123288 | 71923',1 | 23.5 | 5.0 | 11.0 
24 49 | 352 3559 | 116 | 59| 25 49 | 212 | 277 | 50 | 110 
12 | 31.7 | 50 | 110 
il | 
27 16 312 | 317 | 120162 | 28,20 3 
| | 18* 
