The following table gives the results of nearly 700 measurements of the solar radiation constant published in Vol. We draw attention to the close agreement of the solar constant values obtained under these contrasting observational circumstances.
IO SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65
Mr. Bigelow finds from thermodynamic considerations that our solar constant values represent the intensity at about 40 kilometers
REPLY TO THESE CRITICISMS
NO. 4 SOLAR
For each of the days we give in the table above the ratios of atmospheric transmission coefficients found for different ranges of air mass in many .. spectrum points, first, as obtained by comparing the results. found in small aerial masses with those found in large ones, and, secondly, b)' comparing those previously published with those now. The new plots did not include observations of small air masses, thus avoiding any observer bias that might have been caused by viewing them.
OBSERVATIONS OF SEPTEMBER 20 AND SEPTEMBER 21, 1914
65 Second objection.—Considering the great importance attached to Second objection.—Considering the great importance which Mr. attributed by Very and others to observations of solar radiation in large air masses, we have re-examined some of our observations of previous years made in larger than normal air masses. The slight tendency in this direction hardly exceeds the error of determination and must be attributed, moreover, to the deviation of the Bemporado air masses from the value of the secant Z used in our previous publications.
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For zenith distances much greater than 70°, the function secant z must be replaced by another, F(z), representing the ratio of the effective length of the path of the ray in the atmosphere to that corresponding to £=0. This quantity, F(z), has been determined by Bemporad,1 taking into account the curvature of the earth, the A far more important consideration concerns the distribution in the atmosphere of the materials which decrease the intensity of sunlight as the zenith distance increases.
Wilson, the atmospheric extinction for a large part of the spectrum appears to be almost entirely consistent with the requirements of Rayleigh's scattering theory. It gives the following values of the transmission coefficients for dry air (aa\) and for the equivalent of 1 cm. These water vapor coefficients apply to smoothed energy curves and are a measure of the general extinction associated with water vapor, apart from its selective absorption.
Since this gas forms an almost constant percentage of the atmosphere up to a height of more than 10,000 meters, we used Bemporad's F{z) at this wavelength. The slope of the best straight lines was read from the graphs thus obtained, which gives the logarithms of the transmission coefficients. All the details of the above processes have been described and explored in Vol.
26 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65
II of our Annals we have shown in the second part of the work that the results obtained by this method were harmonious with the cruder results obtained by taking into account the meteorological conditions of the earth. Secondly, that our determinations of the transmission of the optical device (and we ourselves admit that these are determinations that are very difficult and only moderately accurate) also do not distort the shape of the energy curve; Third, that the position of the maximum of energy determines the correct temperature of the sun; Fourth, that the total emission of energy from the sun has the same function of temperature as the total emission from a 'black body'.
Far from discrediting the substantial accuracy of our determination of the shape of the solar energy curve outside the atmosphere, we completely disagree with these authors' application of it. First, the shape of the energy curve as determined by us does not agree with the shape of the energy curve of a "black body" at any temperature. Secondly, if the temperature of the sun could be correctly deduced from the consideration of the position of maximum energy in its spectrum, there would also be no reason to suppose that the radiation of the sun bears the same relation to its temperature as the radiation of a "black body". tolerates its temperature.
As for the dependence of solar radiation transmission on atmospheric water vapor, we have used Langley's hypothesis, that is, that there will be no water vapor outside the atmosphere.
30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 true absorption occurring in spectrum lines which are so fine as to
Fowl's investigations into the relationship between transmission coefficients and Lord Rayleigh's theory of skylight showed that their effects will still be eliminated in the same way as the infrared bands were in the research just cited, because the transmission coefficients in such regions of the spectrum will be smaller than they would be if there would be no bands there. We are satisfied that the existence of such bands, even if there were others besides those known to us, would scarcely in the slightest degree affect the value of the solar constant of radiation. We have not determined the amount of energy contained in the extreme infrared part of the "black body" emission, the size and distance of the sun, at 6,ooo° absolute temperature, and add this to what we have ascertained from our spectro-bolometric observations.
Rather, our procedure was to construct a spectrobolometric curve as we found. If the condition of the sun is now such that its infrared radiation distribution corresponds to a "blackbody" at 7000° or some higher temperature, then the actual rate of fall of the infrared curve beyond the region we observe would be faster than that which we assumed it to be. In any case, there is certainly a difference so far down the spectrum that it is completely insignificant in amount.
65. Eighth objection.- As Mr. Very has shown in a recent article that Eighth objection.- As Mr. Very has shown in a recent article that Mr.
SOUNDING BALLOON OBSERVATIONS
If so, how much and why ?
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The angle of the cone is such that all rays must go either directly or by reflection to the sky, not to the earth. Records of 13,000 meters were obtained, but in the absence of the heating apparatus above, the mercury froze and prevented. The knowledge of how such an apparatus as you propose will act in the absence of the sun seems to me almost indispensable.
Very excellent suggestions, four instruments were arranged for daily use and one with a type. Certain corrections of the barometric readings according to temperature have been made by taking into account the temperatures found on other flights, as will appear there. When reading the record, it was attached to a large sheet of cross-sectional paper, with the degree markings of the balloon pyreliometer record lying parallel to the transverse lines on the abscissa.
A fine wire was then stretched parallel to a branch of the zigzag track, and the tangent to match the slope to the grade marks was read on the cross-section paper.
SOURCES OF ERROR
EFFECT OF AIR CURRENTS
- VARIATIONS IN SKY EXPOSURE
- ROTATION OF THE INSTRUMENT
- RATE OF THE CLOCKWORK
We have greatly reduced this source of error, by attaching to the instrument, a flat plate of blackened tin (r, fig. 5), level with the annular copper diaphragms, which admit the light on the aluminum disk. We therefore believe that at the altitude reached by the instrument, namely 24 kilometers, where the air pressure is only one twenty-fifth of that prevailing at sea level, the effect of this source of error will be to increase the pyrheliometer data by about 0.2 percent. In fact, one of the balloon pyrheliometers was blown to pieces, and the copper diaphragms and grating were transferred to pyrheliometer no.
Another source of error, which was not inconsiderable, depended on the rotation of the balloon during its flight, for the instrument did not merely rotate, but swung round a small cone, so that the average angle which the sun's rays made with the surface of the aluminum disc. By measuring the distance between the edges of the broad lines, compared with results found in control experiments made by moving the instrument through known angles, the half angle of the cone during the highest part of the flight was determined and found to be about 9 degrees. It was then calculated that a correction of about 1.2 percent should be added to the readings in addition to that of about 8 percent due to the sun's zenith distance.
At Omaha on July 2, 1914, during calibrations, the average period occupied by a full rotation of the shutter was determined to be 8m 17s;
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HORIZONTAL THERMOMETER STEM AND CALIBRATION
OTHER CORRECTIONS
In all the circumstances, we feel that the various small positive corrections, including the below-mentioned error in determining the angle of rotation of the cone, but not that of pitch or pitch, can be considered to balance the various small negative corrections. Washington, correction for effective solar zenith distance, correction for mean solar distance, correction for tact, and probable correction for attenuation outside the atmosphere.
CIRCUMSTANCES OF OBSERVATION The following circumstances attended the
JULY 9, I914
DISCUSSION OF RECORDS
THE NIGHT RECORD
The lighting current was turned off intermittently to prevent premature shutdown. The lighting power was turned off intermittently to prevent premature battery depletion. It is not evident from the last part of the plate corresponding to A3A±, from which we deduce that the electric heating proved insufficient to maintain the temperature of the disc above about -15, which corresponds to the position C, and that the plate.
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THE DAY RECORD
4 SOLAR RADIATION ABBOT, FOWLE AND ALDRICH 47 Accordingly, we give only the readings on the original. Accordingly, we only provide the readings on the original. The pyrheliometer record consists of a series of zigzag shadow areas corresponding to the up and down marches of the mercury column. We do this because: (1) As mentioned above, the earlier part of the records comes from. little value because the bore of the thermometer is dirty.
A defect in the record occurs just after the balloons began to descend, first due to a jerk, and then due to the intersection of this seam in the newspaper, which makes the next two readings doubtful.
CORRECTION TO REDUCE TO VERTICAL SUN
4 8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 of the degree marks is naturally less wide than it would have been if
READINGS ON
UNITED STATES DEPARTMENT OF AGRICULTURE, Weather Bureau,
4 SOLAR RADIATION ABBOT, FOWLE AND ALDRICH 51HEIGHT OF THE BALLOON, DETERMINED FROM THEODOLITE MEASUREMENTS HEIGHT OF THE BALLOON, DETERMINED FROM THEODOLITE MEASUREMENTS.
CALIBRATION OF THE BAROMETRIC RECORD OF JULY 11, 1914
The barometer element was calibrated by enclosing the entire instrument in a copper box from which air could be blown out, and whose temperature was regulated by immersion in a stirred bath of gasoline cooled by expansion of liquid carbon dioxide. In another set of experiments, both temperature and pressure were simultaneously lowered to match the temperatures and pressures indicated by the preceding results of the Weather Bureau observers. From experiments of December 26, 1914, and February 1 and 4, 1915, we find that the zero of the barometric element changed linearly at a rate of 0.123 mm.
From our examination of the records of various balloon flights at Omaha and Avalon, we assume that this would be considered equivalent to an altitude of 24,000 meters, which.
COMPARATIVE RESULTS OF PYRHELIOMETRY AT REDUCED ATMOSPHERIC PRESSURES
54 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 Peppier intended to repeat the work in 1914 at greater altitudes, but
