352 SECTIONAL TRANSACTIONS.—A.t 
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Mr. C. G. ABBot.—Twenty-five Years’ Study of Solar Radiation. 
This paper deals with the intensity of the energy of the sun’s rays; its losses in 
the atmospheres of the sun and the earth; its inequality over the solar disk; its 
distribution in wave-lengths in the spectrum; the development of instruments and 
methods to measure these phenomena; the variability of the solar radiation ; 
periodicities in solar variation; and the dependence of weather thereon. These 
wide-ranging, yet closely related researches have engrossed investigation for more 
than a quarter of a century. Arranged chronologically, they have yielded the 
following results : 
1. Improved stability and sensitiveness of the recording spectrobolometer. 
2. Accurate values of the dispersion of rock salt. 
3. Mapping of about 1,500 lines and bands of solar and terrestrial absorption in 
the infra-red spectrum. 
4. Development of the silver-disk, the water-flow, and the water-stir pyrhelio- 
meters, which have enjoyed wide acceptance. 
5. Improvement of the fundamental process of solar constant measurement. 
6. Nearly 2,000 solar-constant measurements at Washington, Bassour, Mount 
Wilson, and Mount Whitney from 1902 to 1920, yielding a mean value of 1:94 calories 
per square centimeter per minute and proving that the sun is variable. 
7. Many determinations of the distribution of energy over the sun’s disc for various 
wave-lengths. 
8. Many determinations of the distribution of energy in the solar spectrum, 
yielding estimates of the effective temperature of the sun. 
9. Development of the recording balloon pyrheliometer, and determination 
therewith of the solar radiation at 25,000 meters altitude. 
10. Development of the pyranometer, an instrument for measuring sky radiation. — 
11. A new brief method of solar constant determination whereby five independent — 
values per day are obtained with minimum atmospheric influence. 
12. Daily observations of the variability of the sun at several widely separated 
high-altitude desert stations beginning with the year 1920. 
13. Determination of the march of variation of the monthly mean values of the . 
solar constant of radiation for the past twelve years with an accuracy sufficient for 
all purposes. 
14. Discovery that the sun’s radiation varies in five continuing regular — 
periodicities. j 
15. Indications that the weather is to a considerable degree governed by solar 
changes and is probably predictable therefrom. ; 
16. By-products of the research which include determinations of atmospheric 
transparency, precipitable water, and ozone content. 
Tt is hoped that the apparent connection between solar variation and the weather 
will be verified and will lead to improved methods of long-range forecasting. 
Smithsonian observers are going on with solar radiation studies, introducing such 
improvements as may help to establish a more exact record of the solar variation 
available for all future time. 
Dr. F. J. W. Wuirrie.—The Circulation of Electricity through the Atsno- 
sphere. 
Continuous records of the air-earth current, the current which flows during fine 
weather from the air to the ground, are now available at Kew Observatory, and 
provide new information with regard to the circulation of electricity through the 
atmosphere. 
The potential of the Kennelly-Heaviside layer in the upper atmosphere is of the 
order 310° volts. Over the oceans the air-earth current is of about the same 
strength in the northern summer and the southern summer, so that it may be assumed 
that the mean potential of the K.H. layer is the same at all seasons. On the other 
hand, there is a well-marked diurnal variation, the potential gradient over the oceans 
being 15 per cent. below the mean at 5h. G.M.T. and 20 per cent. above the mean at 
19h. G.M.T. The potential of the K.H. layer must vary in the same way. 
The fluctuations in the air-earth current at a place like Kew, where there is con- 
siderable atmospheric pollution, are governed partly by the potential difference 
between the K.H. layer and the ground and partly by the resistance of the air. It 
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