Читать книгу The Works of Benjamin Franklin, Volume 3 - Бенджамин Франклин - Страница 7

Philadelphia, 18 April, 1754.

Sir:—

Since September last, having been abroad on two long journeys and otherwise much engaged, I have made but few observations on the positive and negative state of electricity in the clouds. But Mr. Kinnersley kept his rod and bells in good order, and has made many.

Once this winter the bells rang a long time during a fall of snow, though no thunder was heard or lightning seen. Sometimes the flashes and cracks of the electric matter between bell and bell were so large and loud as to be heard all over the house; but by all his observations the clouds were constantly in a negative state, till about six weeks ago, when he found them once to change in a few minutes from the negative to the positive. About a fortnight after that he made another observation of the same kind, and last Monday afternoon, the wind blowing hard at southeast and veering round to northeast, with many thick, driving clouds, there were five or six successive changes from negative to positive, and from positive to negative, the bells stopping a minute or two between every change. Besides the methods mentioned in my paper of September last of discovering the electrical state of the clouds, the following may be used. When your bells are ringing, pass a rubbed tube by the edge of the bell, connected with your pointed rod; if the cloud is then in a negative state, the ringing will stop; if in a positive state, it will continue, and perhaps be quicker. Or suspend a very small cork ball by a fine silk thread, so that it may hang close to the edge of the rod-bell; then, whenever the bell is electrified, whether positively or negatively, the little ball will be repelled and continue at some distance from the bell. Have ready a round-headed glass stopper of a decanter, rub it on your side till it is electrified, then present it to the cork ball. If the electricity in the ball is positive, it will be repelled from the glass stopper, as well as from the bell; if negative, it will fly to the stopper.

B. Franklin. Ref. 005