Our Astronomical Column

Abstract

SUN-SPOTS AND WEATHER.—The first part of vol. vi. of “Indian Meteorological Memoirs”(Calcutta, 1894) contains a paper by Mr. W. L. Dallas, Assistant Meteorological Reporter to the Government of India, on the relation between sun-spots and weather, as shown by meteorological observations made on board ships in the Bay of Bengal during the years 1856 to 1879. The region selected offered peculiar advantages for such inquiry. The annual periodic changes in it are small, and the aperiodic changes are very slight. There is also comparatively little horizontal air motion, and, being a sea surface, the area is not liable to the sudden changes which affect a land observatory, and result from irregularities in the elevation of the land surrounding an observatory. The discussion of the pressure observations shows that there are certain points of similarity between barometer readings and the number of spots on the sun. The number of years during which the number of sun-spots exceeded the normal average coincides with the number of years during which the pressure was below the average, and vice versâ, while the maximum pressure differences, whether above or below the average, occur one year after the maximum sun-spot variations in both directions. The same general agreement is disclosed by the discussion of temperature observations, but here again there is the same want of exacerelation. In the case of pressure the curves show that a defect of pressure prevailed during the years in which the relative number of spots was excessive; and an excess of pressure during the time they were at or about their minimum. So in temperature, it appears from Mr. Dallas' investigation, that there exists a general defect when the number of spots is low, and a general excess when the number of spots is high. The indications are, therefore, that years of maxima and minima in a solar cycle are also years of maximum and minimum solar radiation.