266 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
Perhaps the most remarkable phenomenon revealed by the observa- 
tions from registering balloons is the comparatively sudden cessation 
of the fall of temperature at a height which varies from day to day, 
but is roughly equal to 10 kilometers. Above this height, which may 
be regarded as the height of an irregular, but roughly horizontal, 
surface dividing the atmosphere into two regions, the temperature 
at any time varies very little in a vertical direction, showing, on the 
average, a Slight tendency to increase. The lower and upper regions 
are characterized by the terms “ convective ” and “ advective,” respec- 
tively, and the height and temperature of the dividing surfaces are 
denoted by H. and T,. The following table gives the values of 
H,, T., for certain places in Europe: 
cs linet ei g 
Sli |) ues eo all eae 214 o 
ag 4 3 Zz “ Sj 2 qa SI A 
=| 8 Bo) ee aaa RU all Te Sa a ee 
SS teers ian aie ol ven sabi 4 | SB | & | @ 
| 
Be SSS CEES Cccete | 10.6 10.9 10.8 10.8 10.4 9.6 10.6 10.7 10.2 10.7 
4 ee Se EEO ore 16° 16° 18° AC 18° 18° 14° 17° ile 16° 
Number of cases..-} 336 53 32 67 57 28 18 25 24 32 
atisudeseeeere ease — 48° 52° 49° 49° 60° 56° 45° 48° 52° 
There is very little variation for places between latitude 45° and 
latitude 55°, but at Pavlovsk H, is about 1 kilometer below the aver- 
age. Observations made in the equatorial regions show that the 
value of H, there exceeds 15 kilometers, so that there must be a con- 
siderable increase in its value in crossing the limit of the trade-wind 
region, and it appears probable that the equatorial currents and the 
trade winds form a closed system with little interchange of air with 
higher latitudes. 
The annual variation in H., T, is shown by the following table: 
Annual variation in He. 
; F ES S : ae : 
Bolised aol) ah aloe ayerol eS. luerdh obllecesaes 
peer | el Pea ect TES Sly cea 1A Delco al eee a limes 
Mean of 13stations....-.... 10.3 | 10.4 9.1 | 10.1 | 10.5 | 10.7 | 10.9 | 11.4 | 10.4 | 11.9 | 10.8 10.1 
| 
Number of cases Siete eerste 26 22 32 39 31 27 24 61 46° | 38 25 25 
MUNCH: acmimct ccc hoces 10.0 | 10.4 9.2 OF DEF eral || aloe ao i) 1033 | LPS es 11.4 
Number of cases .......... 4 3 6 4 2 4 3 11 i i 8) 2 5 
Strassburg? .-s-ce-sececeess 10.5 | 10.6 9.4 9.4 | 10.6 | 10.9 | 10.8 | 12.3] 10.9} 11.9] 11.0 11.1 
Number of cases ..:....... 5 5 5 5 4 5 4 9 8 6 6 5 
Annual variation in Te. 
ee es el eee ieee 
Sui er le ale alive taal ste eneseall eel fess nome eareanall nics 
aera eh | a eas 
Mean of 18 stations........ 13 11 16 iN || ues 20 20 | 18 22 | 14 15 14 
Miumic¢hyce asc aeccceeceect 14 10 16 19 | 25 20 15 16 26). 19) | 10 12 
Strassburg issess-neeeeeeeee ae a) aK BIE fe alee Per oa |) ali) | Tey || Te 10 
