Survey of Northeast Greenland. 167 
put the percentage of moisture at 70, the temperature at +2, and 
the pressure of the air at 750 mm we get 
hes is Se) 
In this case we consequently get: 
(1 = 5) — (1 + 0.002) (1 -+ 0.002) — 0.999996. 
Even if we presuppose exceptionally unfavorable conditions, the 
error of putting (1 — — 1 will not exceed one unit in the third 
decimal place, which error is quite insignificant in the face of the 
uncertainty which characterizes the determination of 7 (the variation 
of temperature by the metre). 
In this manner we achieve an essential simplification of the 
computation of x. If we put logR — 6.8059 we get 
= = 6748. = (7 + 0.0342). 
In order to compute x we must thus know the quantities b, T 
and 7. In the case of altitudes up to 200 m and 500 m a mean 
value of T and 7 may be computed for the moments at which kite- 
or balloon-ascensions took place near Danmarks Havn, whereas b 
may be computed by means of T and the pressure at the level of 
the sea, which appears from the meteorological observations under- 
taken day by day. In the unfortunately rather few cases, where 
the levellings at the cairns IX and X are undertaken simultaneously 
with kite- or balloon-ascensions, we thus have a means to control 
the determinations of k by computing x. 
As far as the levellings at the “Skerry” are concerned, the state 
of things is more favorable. Simultaneously with eighteen of these 
levellings measurements of temperature were made at the surface 
of the ice and in the crow’s nest of the ship of the expedition. 
These latter were carried out at an altitude of 30 m above the 
level of the sea, which as far as the determination of 7 is concerned 
practically coincides with the fact that the line of vision from the 
Observatory to the “Skerry” lies at an altitude of between 14 and 
16 m. 
The certainty of the determination of 7 plays a vital part in the 
determination of x; the uncertainty of b and T will in this case be 
rather immaterial. If b and T are looked upon as constant and 
equal to 750 mm and 273° respectively we get 
_ 674.8 >< 750 
dx == mora — 6,8 dr. 
