Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.
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3. During the different months, generally, the electricity of the air is more powerful when the sky is serene than when it is cloudy, excepting towards the months of June and July, when the electricity attains its maximum ; the value of which is nearly the same, whatever be the state of the sky. Thus, setting out with these views, the electricity of the at- mosphere during a serene sky exceeds the electricity observed during a cloudy sky, and so much the more as we approach nearer to January. In this latter month the ratio is more than four to one. Now, this powerful atmospheric electric intensity, during the serene sky of winter, is a very remarkable circum- stance. This has been again and again proved by philosophers, who have been especially engaged in observing the phenomenon of atmospheric electricity, but who appear to give it a less rela- tive value. Storms. Mr. Quitman has collected tables of observation made during extraordinary circumstances, such as in times of snows, rains, and fogs. He finds that under certain conditions, a powerful electric atmosphere obtains at the approach of a rain storm, and after a rain storm, which is sometimes positive and sometimes negative. The electric intensity observed during fogs has a mean, the same as that obtained during snows, and is not much influenced by the time of season. The value of electricity observed during a tranquil rain, differs very little from the mean taken in the course of the whole year. The electricity of the air estimated at an elevation always the same, suffers a diurnal variation, which generally shows two maxima and two minima; and these are displaced according to the different epochs of the year. The first happens before 8 o'clock in the morning in the summer, and at about 10 A. M. in the winter. The second maximum is after 9 P. M. in the summer, and about 6 P. M. in winter. The day minimum is found to be about 3 P. M. in summer, but near to 1 P. M. in winter. The night minimum is as yet not so exactly obtained. Observations accurately taken at all even hours Greenwich