Another notable instance of low-lying storm-clouds, and which furnished the rare opportunity of measuring the thickness of one of them, occurred at the city of Gratz, Austria, on June 15, 1826. The city is built along the side of a hill, the highest point of which, called the Schlossberg, has on its summit a castle, now in ruins, but at the time garrisoned by troops, and furnished with a small observatory. When the storm in question broke over the city, several scientific men on the Schlossberg took notes of the movement and direction of the great cloud emitting its electric discharges. This they could easily do, as they themselves, on their altitude, were standing in sunshine, under a perfectly blue sky, the dark cloud-wave rolling deep under their feet, indicating its path and size by streams of fire, following each other in rapid succession. Exclusive of short flashes, vanishing in the air as soon as seen, there fell nine great strokes of lightning upon buildings in the city, in the course of about three quarters of an hour, five of them causing conflagrations and killing a number of people. The storm over, the observers compared their measurements, and it was then found that the height of the storm cloud had never been above the clock-tower of the Johanneum, an edifice connected with the university, and containing a library and museum, while the lowest part of it had gone down the sloping ground of the city no further than 120 feet under the summit of the clock-tower. This, then, was the exact thickness of the storm-cloud which had caused so much destruction. It was noticed on this occasion, as had been done often before, that the discharges of lightning fell all upon buildings standing on moist ground, near the river Mur, a mountain stream coming from the Noric Alps, and dividing the city into two parts. There can be no doubt, from thousands of observations made, that it is one of the characteristics of the electric force to seek its way towards water--to be, as it were, dissolved by it, or, as perhaps it might be said more truly, to be equalised by it. A very remarkable electrical phenomenon, and one which is often attended with fatal results to men and animals, is what is known as the ‘return stroke’ of a lightning discharge. This is always less violent than the direct stroke, but is nevertheless very powerful. It is caused by the inductive action which a thunder-cloud exerts on bodies placed within the sphere of its activity, and disastrous effects often take place upon objects, upon men and animals on the earth under the cloud, although perhaps miles away from the point where the discharge takes place. These bodies are, like the ground, charged with the opposite electricity to that of the cloud; but when the latter is discharged by the recombination of its electricity with that of the ground, the induction ceases, and all the bodies charged by induction return to a neutral condition. The suddenness of this return