Radiation, 
401 
whence x =6.307 the number of actines corresponding to one division 
of the scale of the instrument. 
The method of observation is simple; care being taken to pre¬ 
serve the instrument from draughts of air and gusts of wind, as 
much as possible, and to ensure freedom from penumbral shadows. 
It is first exposed one minute in full clear sunshine, and the effect 
noted in parts of the scale, and then shaded for the same time ; 
alternate observations of the sun and shade being made, until 
quintuple sets, or some convenient number, have been obtained. 
Thus, for example— 
h. m. s. 
1 50 0 
. 51 30 
. 63 0 
. 54 30 
. 56 0 
. 57 30 
. 59 0 
2 00 30 
. 2 0 
Initial. 
Date and times of 
observation. 
Y. D. Land. 1844. 
April 6. 
>—* 
h. m. s. 
1 51 0 
. 52 30 
. 54 0 
. 55 30 
. 57 0 
. 58 30 
2 00 0 
1 30 
. 3 0 
Terminal. 
©XQX0X0X© 
Exposure © 
or Shade x 
to 
CO 
10.0 
25.4 
26.0 
40.8 
41.8 
57.0 
58.2 
73.2 
74.4 
A 
Initial. 
Readings of 
the instrument 
27.0 
19.5 
42.5 
35.1 
58.7 
51.2 
75.0 
67.6 
91.2 
B 
Termi¬ 
nal. 
+ 17.0 
— 5.9 
+ 16.5 
— 5.7 
+ 16.9 
— 5.8 
+ 16.8 
— 5.6 
+ 16.8 
Change 
per 
minute of 
mean 
solar time 
B-A 
\o to w to to JO 
Is? lO W ti) W p 
tlx b\ o b ® 
o © & or O O CM 
Radia¬ 
tion 
in parts 
of 
scale. 
Oi 
ft 
Circumstances very 
favourable for obser¬ 
vation. 
f The time is apparent 
| time, or the ©’s hour 
<< 
angle from the meri- 
Ldian. 
Alt. of © 33° 28' 
Remarks. 
Let © x ©' X' ©" X" ©'" X'" &c., &c., represent the num- 
