580 MONTHLY WEATHER REVIEW DECEMBER, 1924
DORNO ON THE TECHNIQUE OF THE MEASUREMENT OF SOLAR RADIATION IN RESTRICTED SPECTRAL REGIONS I
sir/. s'r By HERBERT H. BIMBALL
[U. 8. Weather Bureau, Washington. D. C., Docember 17, 10241
The first part of the paper, Heft 8, 234-239, ives the
missibility of different glass and Wratten-gelatine filters for radiation of different wave lengths. Such filters have been employed at Davos and elsewhere to isolate solar radiation in rest.ricted regions of the spectrum, so .that the intensity and variability of the radiation at different wave len@hs might be determined under different con- ditions mth respect to weat.hef, seasons, solar altitude, geographical position, etc.
As had been antici ated, Wratten-gelatine filten of
only in a restricted re ion of the visible spectrum, but
disappointing, however, to find that the red and also the blue glass screens of Schott. transmitted ultra-red radia- tion also, as shown in Figure l, and that this radiation could not he eliminated by the use of a water cell 1 cm. thick in conjunction with t-he glass screens.
results of spectro-analytical investigations of t % e trans-
different colors were P ound to transmit radiation, not
also over a considerab f e range in the ultra-red. It was
FIO. l.-Transmlssibility of glass Alters for radiation of different wave lengths
This last result is not in ac.cord with tests made for
the United States Weather Bureau by the United St.ates Bureau of Standards on a combined blue-glass screen (F3873 Schott &- Genossen) 9.58 mm. thick, and a water cell 1 cm. thick, as is shown by the transmission coefficients of Table 1.
TABLE 1.-Transmission of combined bliw-~mss screen (No. F3887.9
Schott & Genossen) and water cell 1 cni. thick. Bureau of Standards
icrsi! No. 3508 -- Wave1endh.u ______ I 348 I 350 I 360 I 370 I 380 I 390 I 400 I 410 I 4% I 430
Transmission,percent) 31 I 30 1 24 I 18 I 11 1 6 I 3 I 110.01-~0.02-
Transmlssion:
1 out to 9,m ##I.
As is pointed out by the author, the resulta of his tests indicate that caution must be used in interpreting measurementa of the intensity of restricted areas of tlie
I C. Dorno, mit Betrllgen von K. W. Meissner und W. Vahle: Zur Technik der Sonnenstrahlungsmessun n in einzelnen Spectraibezirbn (Filterdurchlllssigkeit, ZellenempBndlicbkeit, 8chelson-Actinometer). Met. Zeit., 1924, Heft 8: -23%
HeJt9: 269-m.
solar spectrum where color screens have beeen used. See for exam le his paper in tlie MONTHLY WEATHER REVIEW, Octo \ er, 1922, vol. 50: 515.
This does not apply to measurements by photoelec- tric cells, however, since these cells are not sensitive to ultra-red radiation. The second part of the paper, Heft 9, 269-276, gives the results of tests of the sensibility of photoelectric cells to radiation of different wave lengths. Four cells were tested as follows: two potassium cells, one highly
FIG 2.--Com arison between the sensitivity of the human skin (Curve I) and that of a eahmium (Curve 11). NorE.-This cell, obtsined by Dorno in I=, is less sensl- tive to short-wave radiation than is a similar %il obtained before the war. This is attributed by Dorno to a difference In the glass m the bulbs
evacuated, and one filled with argon gas; two cadmium cells, one large and the other small, the large one obtained after the war, and the small one before the war. otassium cell
length than the evacuated cell, or at about 4 5 0 ~.
The curves of sensibility of the two cadmium cells are quite dissimilar. The one procured before the war is relatively more sensitive to shorbwave radiation than the other, their maxima occurring a t about 2651.~~ and
28Opp, respectively. The difference is attributed to the difference in transmission of the uviol glass of which the walls of the cells are made, and from this it is con- cluded that the true niaxinium of the cadmium cell, if uninfluenced by the glass of the cell walls, would be a t
The results show that the gas-filled has ita maximum of sensibility at a slight P y longer wave
DECEMBER, 1924 MONTHLY WEATHER REVIEW 58 1
a much shorter wave length than that given by these tea&. It follows that the cadmium cell promises to be of great value where measurements of ultra-violet radiation (of shorter wave length than 3 1 3 ~~) are desired. It is shown that this is the case in radio-therapy, since it is this short-wave radiation that is most active in roducing pigmentation of the skin. 8pon this point Dorno says:
Correct dosage is of the greatest importance in all radio-therapy;
so long as the dosage is based upon the degree of pigmentation of the skin there is need for an instrument giving measurement of intensity exclusively for t h a t spectral region which causes pigmen- tation. In Figure 2 are drawn (1) the curve of sensitivity of the skin according to Hausser and Vahle in degrees of pigmentation, and (2) the sensitivity of the cadmium cell, both determined by
quartz lamp radiation. Curve I is displaced somewhat toward the left of Curve I1 and descends more slowly in the lower portion of the right-hand branch. However, i t is apparent that the cad- mium cell almost esactly singles out of this long spectrum of the mercury lamp, extending from about 800 to 230 gn (no account being taken of the ultra-red) olily that very narrow spectral section which is asential, so far as actions of pigmentation are to he measured, and that within this very narrow spectral section there is found practically the same distribution of energy as that desi!- able for evaluating the action upon the skin. Therefore, for use 1x1
radiation cures, which takes into account the degree of pigmenta- tion, there can hardly be invented a better dosimeter than the cadmium cell. If we attach importance to a better coincidence in the two curves of Figure 2, which will hardly be of great importance in the matter of correct dosage, i t is presumable t h a t this could be attained by choosing for a cell wall a uviol glass which offers a
somewhat greater hindrance to the passage of the ultra-violet rays.
Part 3 of the aper, Heft 9 : 276-277 is devoted to a
which has been in use at Davos with satisfactory results since 1909, when two of these instruments were pur-
chased from Moscow. A third was obtained in 1914,
likewise from MOSCOW, and with the three instruments more than a million measurements have been made, at the surface of the earth from sea level to elevations of
3,500 meters, a t sea, and on balloon flights, without damage to the instruments, and with little change in
their standardization constants. Dorno speaks of them as reaching a stable condition within 10 or 15 seconds
after exposure, and following close1 all variations in
correction is required by the first two instruments belon ing to the type described in Physikalische Zeitschrik:
19OS, age 18, and following pa es, whereas the third,
Zeitschrift, 1913, page 577, does not show any greater dependence upon the tein erature than that cited with esamples by Professor hichelson, being thus quite extraordinardy independant of temperature oscillations. The data relatin to the various tests are presented in tables and also in fiagrams.
In preparing this summary the writer has made use of an English text prepared by Dorno. This text included Figure I1 which does not appear in the original paper.
discussion of t f e Michelson bimetallic actinometer,
atmospheric transmission. A not irre T evant temperature
one be P onging to the type describe f in the Meteorologische
THE PROBABILITIES OF 0.10 INCH, OR MORE, OF RAINFALL AT SPRINQFIELD, ILL.
By WALTER F. FELDWISCH
[Weather Bureau. Springfleld, III., August 27,1924 &-ti-//. ti?#. i ( 7731
The great majority of rain-insurance . policies are written on the basis of 0.10 inch precipitation occurring within a specified time. Those who contemplate insuring events frequently inquire of Weather Bureau officials as to what hours during the day rain is most likely to occur, and they especially desire to know the probability of a fall of 0.10 inch or more. Computations showing the avera e relative depth of fall for each hour are very valua%le, but the rate of fall may vary decidedly for the different hours and it may be possible that though rain falls more frequently at certain hours than at others, nevertheless the showers at that particular time of day have a tendency to be so light or of such short duration that frequently the total will not be brought up to the 0.10 inch required to collect the insurance.
Computations have been made for the Springfield, Ill., station, showing the actual percentage of times an amount of 0.10 inch or more of recipitation occurred within
As would naturally be su osed, the table indicates that the greater the number of!ours includecl in a period the greater becomes the robability of 0.10 inch within the
while in May, for instance, in considering sis-hour periods,
one inspecting the total hourly falls as shown by Table 2
andF' ure 1, and the ercentages as shown by Table 3,
6 a. m. better for the insured from a monetary point of
view than those from 12 noon to 6 p. m. by a margin of 2 to 1, provided rates for all hours are equal, never- theless this supposition is not borne out by the figures of Table 1. Furthermore, Table 1 shows that in May there is, on the average, less probability of 0.10 inch oc.curring within six hours following the individual hours 6 a. m. to 11 a. m. than for those of 12 noon to 6 p. m.,while Table 3 shows that a sli htly greater percentage of the
specified time limits, and t R e result is shown in Table 1.
specified hours for t R e different tinies of the day. So,
mightte inclined to t R ink the hours from midnight to
24-hour amount occurs Q etween 6 a.m. and 12 noon
h? 2 4 6 8 &9 h 0 #2 4 6 8 #M
5
4
3
2
$Yvi i i i i i i i i i i i i i i i i i i i i I
5
4
3
2
/
$1
Q 35
*g
h: 2
/
0
4
3
2
/
0
3
2
/
0
FIG. 1.-Total hourly amounts of preelpitation May to October for the 19 years 1906
1923, inclusive, at Springlleld, ill. Data from Tible a