19211 



on Cloudland Studies 



137 



The observations were continued throughout the day ; these and the 

 corresponding values of the Z/E ratio are shown in Fig. 21. The 

 sun displacements are given directly in terms of the readings of the 

 cm. scale, the displacement due to the black body at 15° 0. (full 

 aperture) being 3*0 ± 0*1 cm. The shade temperatures are also 

 included. Xo definite clouds were visible, but a thin persistent drift 

 could easily be detected when the sky was viewed through an amber 

 screen. This was no doubt partly the London smoke haze. 



Similar attempts were made at the time of the total lunar eclipse 

 of May 2-3, 1920. The instrument was, however, then in a more 

 crude condition, and the weather was largely overcast until the 

 eclipsed moon had sunk very low. Succeeding nights were, however, 

 clear, and some comparative measurements were made with and 

 without the full moon in the same aperture of the instrument by 

 directing the mirror to different regions of the sky at the same 

 elevation. The instrument was set up a few feet above the ground 

 in an open meadow some ten miles N.W. from London. A clump 

 of trees obscured up to 15" of the sky above the horizon from the 

 east to the south, while some houses 50 yards away extending from 

 S.W. to W. obscured about two-thirds of this amount. The mano- 

 meter readings for half a minute were as follows, the effective 

 aperture of the instrument being les- than 20" : — 



(1) May 2-3— 



Midnight 

 11.30 p.m. 

 11 p.m. . 

 2.15 a.m. . 



(2) May 4— 



11.15 to 

 11.45 p.m. 



(3) May 5— 



12.30 to 

 1.15 a.m. 



Black body at 8° C. . . 3-0 cm. 



Zenith (clear) . . .1*8 cm. 



Sky zone with full moon . 2*6 cm. 



Ditto with moon eclipsed . 2*25 cm. 



, Black body at 2 C C. . .2-4 cm. 



J Zenith (hazy) . . . 1-9 cm. 



Sky zone with full moon . 2 ■ 95 cm. 



Ditto without moon, 30 ? S. 



of above . . 2 • 50 cm. 



I Ditto without moon, to 



N.NE. (opposite) 2-0 cm. 



(Black body at 0~ C. . . 2-9 cm. 



I Zenith (clear stars) . . 2*15 cm. 



I Sky zone with full moon . 2 -95 cm. 



' Ditto without moon, due S. 225 cm. 



at same 

 elevation 



at same 

 elevation 



From (1) it follows that the additional radiation due to the full 

 moon was - — ~ - of the value for the sky zone alone, or 



0-35 

 2-25 



2-2:. 



3 



2-25 

 0-116 of the black body at 8 C C 



