( 206 ) 
left the choice between June 22 and July 12; and as June 21 
is midway between Febr. 22 and Oct. 17, we have good reason 
for choosing June 22. 
The harmonic analysis of the numbers for the 12 days periods 
yields: 
D=87.1 + 10.2 coz (n X 12° — 24°15')+ 8.3 cos (n X 24° — 67°53’) 
but this formula does not account for the steeply rising maxima, 
which demand the terms with 3 p and 4 p and so reduce the cosine- 
formula to a mere result of calculation. I think it therefore more 
suitable to defer the deduction of formulae until an explanatory and 
acceptable hypothesis has been found. 
DIURNAL VARIATION. 
Hour. Sp ee Hour. Sd A 
0— 1AM | 91 45 0—1PM | 48 2 
1— 2 | 72 26 1— 2 45 —1 
2— 3 59 13 2— 3 46 0 
3— 4 35 —ll do 4 48 2 
4—- 5 19 —27 4— 5 39 —7 
5— 6 ll —385 5— 6 47 1 
6— 7 8 —38 6— 7 95 —21 
7— § 7 —39 7— 8 43 —3 
8— 9 23 —23 S— 9 66 20 
9—10 27 —19 9—10 58 12 
1o—11 46 0 10—11 103 57 
11—12 37 — 9 11—12 110 64 
Hence mean 46 
Principal maximum (110) 11 —12 PM. 
u minimum (7) 7— 8 AM. 
Secundary maximum (49) + 2 PM. 
v minimum (25) 6 — 7 PM. 
The harmonic analysis of the hourly numbers yields: 
S = 46.5 + 24.6 cos (n. 15° — 324°52') + 7.8 cos (n. 30° — 312°33') 
+ 13.6 cos (n. 45° — 8°48’) + 21.3 cos (n. 60° — 331°9’) 
Again the term with 4 @ is very large. One receives the im- 
pression that in the daytime the height of the sun exerts a 
