UPPER AIR—-GOLD AND HARWOOD. 263 
sures, or (2) by testing the thermometer through the temperature 
range at different pressures and the barometer through the pressure 
range at different temperatures. The second is, of course, the more 
desirable plan, but the difficulties involved in applying it to the larger 
tvpe of instrument are so considerable that the former method is 
generally adopted where such instruments are used. The simplicity 
of the smaller type of instrument devised by Dines enables the second 
method to be adopted in testing it without elaborate and expensive 
apparatus. 
Temperature records obtained simultaneously with different instru- 
ments show differences which, in the mean, do not exceed 1° C., and 
the temperatures may, in general, be taken to be correct to this degree 
of accuracy, but lagging of the instruments makes it doubtful if in all 
cases the recorded temperatures and heights actually correspond. 
In dealing with the observations it is found convenient to express 
temperatures in degrees centigrade above the absolute zero, —273° C. 
on the ordinary scale. Where necessary the letter A is used to char- 
acterize this scale. Atmospheric temperatures, both at the surface 
and in the upper air, lie almost always between 200° A and 300° A, 
so that the 2 may be dropped without risk of confusion. Gradients 
of temperature are expressed in degrees centigrade per kilometer, and 
are reckoned +- when temperature decreases upward. 
The mean value of the gradient up to 3 kilometers is as follows: 
Degrees. 
From the Berlin manned balloon ascents, 1888-1897______________________ al 
From the Berlin manned balloon ascents, 1897-1907_.____-_-______________ 4.8 
Hromeihe Berlinvand windenbersskitesascentse = a ee ea 4.7 
Calculated by Hann from mountain observations___---___________________ ay, Uf 
It follows from these results that the mountains are colder than the 
free atmosphere at the same height, and maney observers have verified 
this fact by direct comparison. Shaw and Dines found that in July, 
1902, the temperature on Ben Nevis was 2.6° C. below that of the free 
atmosphere at the same height to the west of the mountain. Schmauss 
found that the temperature on Zugspitze (nearly 3,000 meters), which 
lies on the northern edge of a mountainous region, was continually 
lower than that of the free atmosphere, but was higher than that at 
the same height on Sonnblick, which hes in the middle of the Alps. 
It was pointed out by Von Bezold that increase of temperature on 
a mountain is limited by convection, whereas no immediate limit is 
set in this way to cooling. There is a one-sidedness in the heat 
exchange between the mountain surface and the atmosphere which 
would tend to produce the result found by observation. Moreover, 
convection always tends to raise the temperature of the upper air 
above what it would be otherwise, and in addition the cold of winter 
is, as 1t were, stored up in the snow, while no such process holds for 
45745°—sm 1909——18 
