An epitome of electricity & galvanism

by Jacob Green; Erskine Hazard

The string of the kite was now fastened by a silk string to a post in the yard of the house; I was repeatedly charging two phials, and giving shocks with them: while I was so doing, the electricity, which was still positive, began to decrease, and in two or three minutes it became so weak, that it could hardly be perceived, with a very sensible cork ball electrometer.—Observing at the same time that a large black cloud approaching the zenith, (which no doubt caused the decrease of electricity) indicated rain, I introduced the end of the string through the window on the first floor, where I fastened it by the silk to an old chair.—The quadrant electrometer was set upon the same window, and was, by means of a wire, connected to the string of the kite. Being now three quarters of an hour after three, the electricity was actually imperceptible, however in about three minutes it returned, but now upon examination, it was found to be negative, which was evidently occasioned by the approach of the cloud, which by this time had reached the zenith of the kite; the rain also began to fall in large drops. The cloud came farther on, the rain increased and the electricity keeping pace with it, the electrometer soon arrived at 15°. Seeing now that the electricity was strong, I began again to charge the phials and to give shocks with them; but the phials had not been charged more than three or four times, before I perceived that the index of the electrometer was arrived at 35°, and was still rising. The shocks now being very smart, I desisted from charging the phials, and considering the rapid advance of the electricity, thought to take off the insulation of the string, that if it should farther increase it might be conducted silently to the earth, without occasioning any bad accident.

To effect this, as I had no proper apparatus near me, I thought to remove the silk string, and to fasten the twine itself to the chair. I disengaged the wire which connected the electrometer with the string; untied it from the silk, and fastened it to the chair: but while I was effecting this, which took up less than half a minute, I received twelve or fifteen very strong shocks, which I felt all along my arms, in my breast, and legs, shaking me in such a manner that I had hardly power to effect my purpose, or to warn the people of the room to keep their distance. As soon as I took my hands from the string, the electricity (in consequence of the chair being a bad conductor) began to snap between the string and the window shutter, which was the nearest conductor. The cloud was now just over the kite; it was black, well defined, and nearly of a circular form, its diameter appearing to be about 40°; the rain was copious but not remarkably heavy.

As the cloud was going off, I went near the string, and finding the electricity weak, but still negative, I insulated it again, thinking to keep it up some time longer; but observing that a larger and denser cloud was approaching, I resolved to pull the kite in; accordingly a gentleman, who was near me, began pulling it while I was winding up the string, he told me he had received two or three slight shocks in his arms, and if he should feel one more, he would let the string go; upon which, I pulled the kite in as fast as I could myself, without any further observation, being ten minutes after four o’clock.

N. B. There was no thunder or lightning perceived that day, nor for some days before, nor afterwards.

The general laws which Mr. Cavallo deduced from a variety of experiments made by means of electrical kites, are the following:

1st. The air appears to be electrified at all times; its electricity is always positive and much stronger in frosty than in warm weather; it is by no means less in the night than in the day time.

2d. The presence of the clouds generally lessens the electricity of the kite, sometimes it has no effect upon it, and it sometimes, though rarely, increases it a little. To this the above mentioned instance is a remarkable exception.

3d. When it rains, the electricity of the kite is generally negative, and very seldom positive.

4th. The aurora borealis seems not to affect the electricity of the kite.

5th. The electrical spark taken from the string of the kite, or from an insulated conductor connected with it, especially when it does not rain, is seldom longer than the quarter of an inch; but it is exceedingly pungent. When the index of the electrometer is not higher than 20° the person who takes the spark will feel it in his legs; it appearing more like the discharge of an electrical jar, than the spark taken from the prime conductor of an electrical machine.