However, the phenomena of atmospheric electricity, which have become noticeable since the use of wire, may be described here. Generally, whenever the kites rise above seventeen hundred feet, the wire becomes strongly charged with electricity, and when the great heights are reached the electricity is discharged in long and brilliant sparks at the reel, often to the inconvenience of the attendants. Usually, the electrical potential increases with altitude, and it is greatest during snow-storms or when the conditions favour thunder-storms. Notwithstanding its intensity, the quantity of electricity in the atmosphere is probably insufficient to make its collection and storage for practical purposes worth while. It must not be imagined that kite-flying for meteorological purposes is a sinecure. At Blue Hill about two hundred flights have been made in all seasons and in all weathers, with temperatures varying from -5∞ to +90∞, in gales, in rain, and in snow-storms, though not in thunder-storms. Sometimes the kites are invisible from almost the time they leave the earth until their return, but when the upper kites are visible it is necessary to observe them with theodolites every few minutes. Remembering that a high flight occupies ten or twelve hours, and frequently terminates late at night, or even continues until morning, it will be obvious that the work requires skill, energy, and perseverance, which have been shown by my assistants at the Blue Hill Observatory who have conducted the flights. Occasionally, for lack of wind or from breakage of the line, the kites fall to the ground, usually intact. If they were visible, trigonometrical measurements on the hill enable the place of descent to be located, and then the kites and meteorograph are sent for and the wire is reeled up. But at night, or when clouds hide the kites, the direction in which they fall is not known, because the azimuth of the wire at the reel often differs from that of the kites; so last autumn several hundred miles of road, path, wood, and swamp were traversed before the aÎrial apparatus, which had been lost during a flight at night, was found comparatively close at hand.