LIGHT 57 
approximately) ; between 8:00 a.M. and 4:00 P.M. the range in intensity is 
from .go to .98 merely. On December 22, the greatest intensity is .52, the 
least .20 (the latter at 8:00 A.M. and 4:00 P.M. approximately). If the grow- 
ing season be taken as beginning with the 1st of March and closing the ist of 
October, the greatest variation in light intensity at Lincoln within a period of 
10 hours with the meridian at its center (cloudy days excepted) is from .33 to 
.98. In a period of 8 hours, the extremes are .65 to .98, i. e., the greatest 
variation, .3, is far within the efficient difference, which has been put at .g. 
On 
Ar fs us 
70 ud 9 a 
noe 
7A 2s 
* i et ZN NK h - - - 
ak KN i Q’witude [Intensity 
i at 70° 4000 
=D Py NN Sas io, ; 796 
a SOAS a “ges 
3 SSSA 8 b 968 
ro “SI J AA \ so 932 
4 ; = eS . 40 909 
Est J 30° 78H 
MS 
77} — — ‘4 20 ata 
ee =: ON 70 234 
‘ 7 nL NOUNAANAANAA i 
40° i WIN NNN 4 
— V3 — aN N\ SSN 
~ ars = NI ENSAANS 
2. i L KON KOA RAARK 
oe BARR2 2 PS Ds aN NNAS ANAK 
a0 Ee im a AASSORAASS gf 
tel —Paeet Pps | PN INONIN AANARSAA 
= Jena AINAIN KAKANAA 
Beets EOR a aN BN SOK SS 
ee n& IN N NAY N w 
20° SANT AKT S AINA ANS * 
SSS SNITATNOATAAAA ANA ANS é 
INNS AY mM EAN ANS 
SIAN NA NOK ANARASATNNIANSAISSY 
NAAN ON NOKAARNINN ASSO 
10° SSS SW IANACIANIANAS aN ) " 
N ANACANACAASS ~ ? 
SAWAANSNORIN SAOATN SORA, j 
“AAA AA SAN aN NAS 
tele RAANINA AN ACANSN 
°° LA San KN 
; ah ah 2h 4h sh e 7h 
Fig. 13. Chart for the determination of the sun’s altitude, and the corresponding light intensity. 
For the growing period, then, readings made between 8:00 A.M. and 4:00 P.M. 
on normal sunshiny days may be compared directly,. without taking into ac- 
count the compensation for the sun’s altitude. Until the efficient difference 
has been determined for a large number of species, however, it seems wise to 
err on the safe side and to compensate for great differences in time of day 
or year. In all doubtful cases, the intensity obtained by the astronomical 
