268 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
occur where the velocity decreases with height. The velocity for 
heights up to 10 kilometers is given approximately by the equation 
Ve=V.p. (Egnell’s law), where V is velocity and p density, Vop, 
being the values near the surface. The law implies that the pressure 
gradient remains constant and independent of the height. Now, 
owing to the fact that the temperature is higher over regions of high 
pressure than over regions of low pressure, the ratio of pressure 
gradient to density increases with height. The condition for a con- 
stant gradient up to 8 kilometers is approximately 
74 0; 
— oa degrees C.., 
where ¢, is the excess of the mean temperature of the air-column at a 
place at pressure ptép above that at a place at pressure p. Observa- 
tions show that for 5»=20 millimeters, 7,=4° C. nearly, or double the 
amount necessary for constant gradient. It is to be expected, there- 
fore, that Vp will increase up to 8 kilometers, and the few pilot- 
balloon observations available point to such an increase. 
The direction of the upper wind usually veers from that at the sur- 
face. The following table shows the deviations for winds from dif- 
ferent quadrants in England and at Berlin: 
Deviation of the upper wind. 
ENGLAND. 
Heights. 
Direction. ee ae 
0.6 km. | 1.0 km. | 1.5 km. | 2.0km. | 2.5km. | 3.0 km. 
fe} Oo fo} oO fe} fe) 
WiGSEiketee a een ae aioe ccinanc le acenmrsies 9 14 14.5 14 8 8 
INOTUR Re ee ce ee Re PEE 4 8 3 —1 — —15 
Wast ress os seen nas apa aon eee 15 22 20 28 35 21 
DOUGH SEM ee Sener coc ce ae as ome meres 14 26 32 38 41 50 
BERLIN. 
fo} oO ° ° co] ° 
WiCSiiren seas ace Sects eee ne See ne ee 18 23 23 20 23 22 
INORtn SS! Sees ee eee eee eee eee 13 17 20 20 15 25 
TOS ola e Ree eae eee oe oe eae aS Ree aa 27 30 38 45 46 44 
Soutbe. eae eo Sie eset eee ee, 38 46 48 49 53 46 
The deviation at Berlin is in nearly all cases greater than in Eng- 
land, especially for north winds, which back slightly in the upper air 
in England. 
There is no marked difference between anticyclonic and cyclonic 
conditions in the change of wind velocity and direction with height. 
