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wind blowing past C and the graduated stem D, which are shaded from the sunshine, or which may be kept immersed in melting ice, although this is not done at Montsouris. In order that the record of liquid condensed in C and D may be proportional to the heat received by A it is necessary that the volume of condensed liquid be independent of the temperature of the air and of the volume of liquid remaining in the bulb A, and be controlled only by the excess of radiant heat received by A over that received by C and D.
The comparisons that have been made at Montsouris between this Bellani radiometer and the Marié-Davy actinometer, or the so-called conjugate thermometers, show that the Bellani apparatus does not perfectly satisfy the theoretical conditions, but as it is extremely sensitive, since it distills 16 or 17 centimeters daily, and as the apparatus is not costly, Descroix has devised a formula for reducing its results to a standard. The following table gives the results of actual observations, showing the average results for the middle portion of perfectly clear days at Montsouris, near Paris, monthly during the growing seasons of 1885 and 1886. The column N shows the number of clear days; V, the volume of alcohol distilled over from 9 a. m. to 3 p. m. on these days in the Bellani apparatus; t, the average temperature of the air in the shade; T2, the average temperature of the black bulb thermometer in vacuum in the sunshine; T2, average temperature of the bright-bulb thermometer in vacuum in the sunshine; T, -T, is the average difference of these conjugate thermometers at midday; R, total illumination from the sky at midday, expressed in Marié-Davy's actinometric percentages or degrees. Comparison of actinometric results for perfectly clear days at Montsouris, near
Paris, by the Bellani radiometer and by the Arago-Davy actinometer.
Notwithstanding the simplicity of Bellani's apparatus and the ingenuity of the idea embodied therein it is evident that it needs an important modification, viz, the evaporation and condensation should
be absolutely independent of the temperature of the air and the velocity of the wind, as well as of the quantity of liquid in the bulb A, and should depend wholly on the heat received from the sun and sky. In its present form it can not be recommended as a simple means of measuring the daily sum total of radiation from the sun and sky. A second and improved form of Bellani's apparatus has been brought out under the title “ Vaporization lucimeter” (see Marié-Davy, Annuaire, 1888, p. 207), but further improvements are necessary, especially the maintenance of a uniform constant temperature in the condensation bulb and tube, as, for instance, by immersing both in a bath at melting point of ice.
ARAGO'S CYANOMETER AND DESAINS' THERMO-ELECTRIC
Other methods of observing the condition of the sky and solar radiation have been devised by physicists. Thus the cyanometer of Arago, especially in the modified form made by Dubosc, of Paris, or the thermo-electric actinometer of Desains (both of which are in occasional use at Montsouris) give useful indications. The cyanometer gives the blueness of the sky, which is largely dependent on the number and size of the particles of moisture, while the actinometer gives the quantity of heat that penetrates directly from the sun through this moist air to the ground. These instruments are complementary to each other, but can only give good results in the hands of those accustomed to the use of delicate apparatus. They serve as checks upon the records of the Arago-Davy actinometer, which latter has been made by Richard in such form as to keep a continuous register. Thus during the years 1879–1886 the Arago-Davy instruments, both in France and in India, showed a steady, progressive diminution in the intensity of the solar radiation received at the ground, followed, however, by a recovery, subsequently, which is not likely to have been due to any instrumental peculiarity. This peculiar fluctuation may have had its cause either in the sun or in the earth's atmosphere.
DURATION OF SUNSHINE.
Those who can not undertake the labor of observing the heating or chemical effects of the solar radiation can easily keep a photographic register of the number of hours of sunshine, as in the apparatus devised by Jordan, of England, and modified by Marvin for use at Signal Service stations, or can keep a record of the hours of full hot sunshine, as in the Campbell, or Campbell-Stokes, sunshine recorder used in Canada. The Marvin photographic sunshine reg
a This paragraph, written in 1891, is of special interest in connection with the general interest in the subject awakened in 1903 by the observations of Kimball, Dufour, and Abbott.
ister has been established at 20 Signal Service stations, the list of which is given in our tabular data. This tabular matter is omitted from this present edition, and these records will undoubtedly be so fully published as to be available to the student. Such photographic sunshine records are complementary to the ordinary record of cloudiness and of personal observations of the area apparently covered by clouds. But as the photographic register, strictly speaking, records only the cloudy condition of the sky in the immediate location of the disc of the sun, while personal estimates of the amount of cloudiness refer to the whole sky (above an altitude of 15°, 30°, or 60°, according to the various rules adopted by observers), therefore there is room for quite a discrepancy between the personal and the photographic record, and it is still a question as to which is more appropriate for agricultural study.
In order to know the cloudiness, sunshine, and rainfall at a few stations representative of the district in which cereals are grown in America, I have added to the stations in the United States, which will be published by the Signal Service, the following table for 1887 compiled for Winnipeg, Manitoba (lat. N. 49° 40', long. W. 97° 10'), from the data published by Carpmael (1890), from whose report other records may be obtained.
Sunshine and climate of Winnipeg.
of total possible.
a.m. a. m.
a Elaborate comparisons of these records were published from month to month in the Monthly Weather Review during 1892–1897.
In the above table the records of sunshine are, of course, given by the self-registering method and relate to duration of visibility of sun at the station, while the cloudiness is the average of the observer's estimates of area of sky covered.
TOTAL POSSIBLE DURATION OF SUNSHINE BY DECADES.
Tables showing the times of sunrise and sunset, or the resulting length of the day, are given is publications accessible to American readers, as follows: Meech, 1855, pages 57, 58, calculated especially for the year 1853; Schott, 1876, pages 117-119, computed for an average year and for the actual sunrise and sunset and for each degree of latitude; the Smithsonian Meteorological and Physical Tables, fourth edition, 1884, give a very convenient table on pages 711-720, by Prof. W. Libbey, computed with the declinations for Greenwich mean noon for 1862; elaborate general tables are given in the International Meteorological Tables, Paris, 1890, but they are not so convenient for our use as the Smithsonian tables or those of Schott.
By means of these tables of sunrise and sunset I have computed the accompanying table, showing the sum total of the possible sunshine expressed in hours from the beginning of January up to any date in a common year or a leap year. From this table has been made up the column of maximum sunshine in the tables of meteorological results for 1879 at twenty stations in the United States as given in Section II for comparison with the crops of that year, as reported in the United States census for 1880. In the absence of any other data
a The annual sums for December 31 in the table are about one-third to onehalf per cent smaller than the figures given in the Weather Bureau table of 1905.
All these manuscript statistical tables are omitted in the present edition.
one may multiply the duration of sunshine by the percentage of observed clearness and obtain the duration of sunshine for a special station. But this will give us a value that is greater or less than the value of the true intensity of sunshine according as the cloudiness occurs mostly in the morning and evening or in the midday hours. The only method for obtaining a satisfactory value of the intensity of radiation as coming direct from the sun or as reflected from the sky, the clouds, and the earth, is to maintain a self-registering actinometer or, in place of that, frequent daily observations.
In these tables I have adopted the division of each month into three parts, as done by Libbey and occasionally used by meteorologists, but the system of pentades, used by Dove, is often preferable; however, this present system is convenient for monthly summations, and is also used in the climatic table of Section II.a
Sums total of possible duration of sunshine, in hours, from January 1 up to any
day of the year.
Hours. | Hours. Hours. Hours. | Hours. Hours. Hours. 10 106.7 105.4 104.0 102.5
99.4 97.7 10 214.5 212.0 209.3 206.4 203.5 200.4 197.2 11 334.7 331.0 327.1 322.9 318.7 314.2
309.5 10 446.0 441.4 436.6 431,4 426.2 420.6 414.9 10 559.4 554,1 548.6 542.6 536.7 530.2 523.7
8 649.9 645.2 640.3 633.9 627.6 €20.6 613.6 10
767.4 762.4 757.2 750.5 743.8 736.4 729.0 10 887.2 882.1 876.8 870.0 863.2 855.7
848.2 11 1,021.7 1,016.8 1,011.7 | 1,005.0 998. 4 991.1
983.7 10 1,146.4 1,141.9 1,137.2 1,130.9 1.124.7 | 1,117.9 1,110.9 10 1,273.3 1,269.4 | 1,265.3 | 1, 259.7 | 1,254.2 1,248.1 | 1, 241.8 10 1,402.3 / 1,399.2 1,396.0 1,391.3 1,386.7 1,381.5 1,376.2 10 1,533.3 1,531.2 1,529.0 1,525.4 | 1,521.9 | 1,517.9 1,513.8 10 1,666.0 1,665, 1 | 1,664.1 1,661.8 1,659.6 1,657.0 1,654.3 11 1,813.6 1,814.1 | 1,814.6 | 1,813.8 | 1,813.2 1,812. 4 | 1,811.4 10 1,948.8 1,950.7 1, 952.7 | 1,953.4 | 1, 954. 4 1,955.3 | 1,956.0 10 2,084.5 | 2,087.9 2,091.4 2,093.7 2,096.3 / 2,099.0 2, 101.5 10 2,220.2 2,225.1 2,230.1 | 2,234.0 2,238.2 2,242.7 | 2, 247.0 102, 355. 4 | 2, 361.7 | 2, 368.2 2.373.6 2,379.4 2,385.6 2,391. 6 10 2,489.7 2,497.3 2,505,2 2,512.0 2,519.3 / 2,527.1 2,534.7 11 2,636.0 2,644.9 2,654.1 2,662. 3 2,671.0 2,680.4 2,689.6 10 2,767.1 2,777.1 2,787.3 2,796.6 2,806.4 2,817.0 | 2,827.5 10 2,896.3 2,907.1 2,918.1 2,928.32, 939.0 2, 950.6 2,962.1 11 3,036.1 3,047.5 3,059.2 3,070.2 3,081.7 3,094.1 3, 106. 4 10 3, 160.8 3,172,6 3,184.7 | 3, 196.1 3,208.0 3,220.9 | 3,233.6 10 / 3,283.2 | 3,295.2 3,307.4 3,319.0 3,331,1 3,344.23, 357.1 10 | 3, 403.3 | 3,415.2 3,427.4 | 3, 439.0 3,451.0 | 3, 464.0 3,476.9 10 3,521.1 | 3,532.7 | 3,544.6 3,555. 9 3,567.6 3,580.2 3,592.8 10 3,636.6 3,647.7 | 3,659.1 3,669.9 | 3,681.0 3,693.0 3,705.0 11 3,761.2 3,771.5 3,782.1 | 3,792.1 | 3, 802.3 3,813.4 3,824.5 10 1 3,872.3 | 3,881.7 | 3,891.3 | 3, 900.3 / 3,909.4 / 3,919.4 | 3, 929. 4