DEOEMBEB, 1914. MONTHLY WEATWR REVIEW. r.l 653
candles in June to 3,600 foot-candles in January. It is leas than the direct solar iUumination on a normal sur- face from September to February, inclusive, but exceeds the latter from Ma to August, mclusive, for a period of
The illumination on a horizontal surface from a coni- pletely overcast sky may be half aa great as the total illumination with a clear sky, and is frequently one-third as great. On the other hand, during severe thunder- storms at noon in midsummer, the illumination may be reduced to less than one per cent of the illunimation with a dear sky. The ratio of sky-li ht illumination to total illumina-
varies from one-third to one-tenth. In midwinter it varies from one-half to onefifth. When the sky is clear the twilight illumination on a horizontal surface falls to 1 foot-candle about half an hour after sunset, or when the sun is about 6 below the horizon.
from four to eight K ours in the middle of the day.
tion on a horizonta f surface at noon in midsummer
1 REFERENCES.
(1) S h 2 Clayton E. 8 Millar, Preston S. A new univeml pho- bmeter. lectrician, 1908, 60:56!2-565. (2) See Bulletin of the Mount Weather Observatory, 1913, v. 6, pt. 5,
p. 218-219; and MONTHLY WEATHER REVIEW, March, June, and Sep- tember, 1914, 42:139,310 and 520. 3 MONTHLY WEATHER REVIEW, August, 1914, 42:480.
{I 4 Annals of the Astrophysical Observatory of the Smithsnnian Institution, Washington, 1913, i3:135-138. Smithmnian Phyma Tables, 6th ed., 1914, p. 182. , , ;f r -
HEAT FROM THE STARS.
In the MONT~Y WEATHER REVIEW for June, 1914 (p. 347), were presented some figures expressing the amount of heating at the earths surface which may properly be attributed to the radiation received from the planeta of the solar system. Equally interesting is the similar question concerning the stars, those innumerable suns lying far beyond our own rime source of heat and
thls problem, and first by constructing an exceedingly delicate radiometer. His instrument is essentially a bis- muth-platinum, or a bismuth-bismuth plus tin alloy ther- mocou de exposed in a high vacuum. He has measured
jects, and finds that red stars emit from two to three times as much total radiation as blue stars of the same photometric magnitude.
Measurements were made on the transmission of the radiations from stars and planets throu h an abso tion cell of water. By this means i t was ahown that, of $e total d a t i o n emitted, the blue stars have about two times as much radiation as the yellow stars, and about three times as much radiation as the red stars, in the spectral region to which tlie eyeissensitive. * * * Measurements were made to determine the amount of stellar radia- tion falling upon l square centimeter of the earths &e. It was found that the uantity is so mall that it would require the radiations from Polaris fa%ng u on 1 square centimeter to be absorbed and con- served continuously g r a period of one million yearn in order to raise
the temperature of 1 gram of water lo C. If the total radiation from all the stars fallin upon 1 quare centimeter were thus collected and con- mrved it waul% require from 100 to 200 years + raiee the tem erature of 1 gram ef water 1 C. In marked contrast wlth this value, $e solar rays can produce the eame effect in about one minute.
energy. Among others Dr. W. k . Coblentz has attacked
the ra b iation from 105 stars, among other celestial ob-
1 Coblentz, W. W. A comparison of stellar rsdiometers and radiometrb mwure- mats on 110 stars. Abatmd in Jour. Wash on BC. sci Washington, Jan. 19, 1915
6: 33-31. Detailed paper will appear b t4e i&$et&t of #;U. 6, Bureau of Standards:
. q.Li2
-4 2 .
E. 5 O N ON T EXTINCTIOm OF LIGHT IN THE TER- RESTRIAL ATMOSPHERE IN THE REGION OR TBg
ULTRA-VIOLET.
By WILHELM S C H Y I ~.
Krons report deals with photographic-photometric observations, b means of a quartz spectro raph, on the
Observatory at fotsdam, Germany, during the years 1911 to 1913. The estraordinary range [Abstufungs- moglichkeit] permitted by the conditions of the experi- ments enabled the region of accurate measurements to include both the estraordinaiy differences in intensity in the different spectral regions (between wave-lengths 430,up and 310pp) and the total solar intensity as related to its altitude above the horizon (measurements being possible down close to it). There is nothing new in the methods of computation which are based upon the Bouguer Formula and Benipornds values for the air masses. In general it appears that the coefficient of transmis- sion p is subject to variations from day to day, while the observations for the same day show good agreement among themselves with de artures due to increased ab-
pected if masses of vapor occur. The mean values ob- tained by Kron are in part essentially lower than those secured in 1909 and 1910 by C. G. Abbota on Mount Whitney; as the following comparison shows. The third column of values have been reduced to Potsdam baro- metric conditions by multiplying.
values for the coefficient of atmospheric transmbsbn, p, by Kmn (Pots- dam) and Abbot (reduecd to Potsdam).
brightness (He z i keit) of the sun at the &3trophysical
sorption for the lowest so Y ar altitudes as would be ex-
Since only the last of the Abbot values seems to have been increased by the action of diffused light in his in- strument, it is at least evident that values determined for a high-level station can by no means be directly re- duced to low-lying stations. Rayleigh is the authority for the assumption that it is particularly the absorption in the region of the shortest wave-lengths (escept certain bands, e. g. those due to ozone, below 0.3251.0, which is produced by scattering from air molecules so that its amount is inversely pro- portional to the fourth power of the wave-len th, 1. If one computes from %ons observations the a % sorption- coefficients C=log nat p, then they may be readily rep- resented by a fomula of the form
(r
C=-+p P
where n=0.01335 and p=0.066. The small value of /3
at once shows the formula closely in agreement with the above law, while this agreement is yet further improved
1 A panslation of a revlew in Met. Ztschr., Braunschweig, Novemlm, 1914,81: 655-8.- c. A. jr.
Washington, 1914, 
Annals of the Qstrophysical Observatory oi the Smithsonian Institution, wl. 3,
654 MONTHLY WEATHER REVIEW. DEOEMBEB, 1914
if one assumes that p expresses the absorption duo to fore' n constituents of the air which may be responsible
Now it is possi le to demonstrate that Rayleigh's law holds ood for these forei n constituents also, that
va or is the first to occur to us in this connection,
rm 3 for this element F. E. Fowle has already devised
.a formula similar to that previousli suggested. Eni- ploying his figures and expressin t e amount of the water vapor w in centimeters o f the equivalent pre- cipitated water, then n = 0.00589 + 0.00067~~ p = O.Ollzcr,
and these well represent the observations, particularly
r3
for t l% e day-to-da variations.
they L o function by mo f ecular diffraction. Water
the general mean of all, with the exception of very sli . ht variations. L o n summarizes his results as follows: The extinction in the region of the ultra-violet up to
0.325 1 may be wholly explained by molecular diffraction , togetfier with the absorption by water vapor which is itself chiefly due to molecular refraction as found by Fowle. Beyond the wave-length 0.335~ his observations re- veal an increase in the extinction which is wobablv due to the influence of tho ozone band here begirking toymake itself felt .
J Ast.rophysical journal, 1913, 88: 302; Meteorol. Ztscbr., 1914, 81: 270. Monthly Weather Review.