——— a re 
PRESENT STATE OF OUR KNOWLEDGE OF THE UPPER ATMOSPHERE. 107 
The following table illustrates this :— 
Layer in | Decrease Velocity in 
Date Place [PtP ETc which Wind | in Advective 
| Decreased | Velocity Region 
| km. km. | m.p.8 | m.p.s. 
July 28,1908 | Ditcham 12 11 —13 18 i 
July 29, ,, | $ ; 13(?) 12 - 13 9 13 
July 31, ,, a | 12°5(?) 11 —13 | 6 27 
Heby 6, >,, | Munich | 12 11 -13 | 15 18 
July 2, ,, > | 11°6 12 — 16 10 7 
Ghee sis) || b | 13:2 11-6147 | 8 8 
On July 31 and September 30, 1908, the velocity was observed up to 
12°9 and 13°6 km. respectively, and showed no falling off, but a steady 
increase. The values of H, were 13°2 and 13°6 km. There is little doubt 
therefore that the falling off in velocity is associated closely with the 
advective region. 
On July 28 the maximum wind at Ditcham was 24 m.p.s. from N.N.W., 
and at Munich on the same day the wind at 12 km. was 21 m.p.s. from 
N. by W., indicating that the current extended right across the intervening 
region, just beneath the advective region. 
The attempts to furnish a reasonable explanation of the phenomenon 
on theoretical grounds led to various suggestions. Trabert' showed that 
if there were a decrease of temperature in a horizontal direction in passing 
eastwards over Europe, and if the air moving eastwards also had a small 
ascending motion, then the adiabatic fall of temperature would not exist 
in a vertical direction. It appears probable, however, that the causes 
which produced a horizontal decrease of temperature in one layer would 
also produce a similar decrease in the layer above it, and in that case 
Trabert’s effect would vanish. 
Fenyi’? considered the question of the absorption of solar radiation 
in the upper atmosphere. He concluded that, if the phenomenon were 
due to this, there must be absorption of dark radiation, since the ultra- 
violet radiation would be insufficient even if it were all absorbed. 
Humphreys * pointed out that if the effective radiating power of the 
earth and atmosphere were the same as that of a black body at tempera- 
ture T,, the effect on any radiating and absorbing matter near enough to 
the earth for the radiating surface to be regarded as an infinite plane 
would be to keep the matter at a constant temperature such that the 
radiation from it would be half the radiation from it at temperature T,. 
If the radiating matter were such as to admit of the application of Stefan’s 
law, its temperature would be T, where T! = 3T,'. 
The observed value of T agrees with the value deduced from this 
equation by giving T, the value estimated by Abbott and Fowle‘ from 
the value of the solar constant, regard being paid to the proportion of the 
incident solar radiation which is reflected and does not affect the tempera- 
ture of the earth. 
Gold ® developed a theory based on the experimental results for 
_ atmospheric absorption obtained by Paschen and others. His argument 
' Met. Zeit., 1907. 2 Thid., 1907. 
8 Astrophysical Journ., 1909. 
* Annals of Observatory of Smithsonian Institution, vol. ii. 
° Proc. Roy. Soc. A., vol. 1xxxii. 
