Perhaps the most distinct and satisfactory evidence on this subject, derived from actual observation, is contained in the following letter of Professor Tyndall, written in May, 1883: “Looking to the south and south-east from the Bel Alp, the play of silent lightning among the clouds and mountains is sometimes very wonderful. It may be seen palpitating for hours, with a barely appreciable interval between the thrills. Most of those who see it regard it as lightning without thunder--Blitz ohne Donner, Wetterleuchten, I have heard it named by German visitors. The Monte Generoso, overlooking the Lake of Lugano, is about fifty miles from the Bel Alp, as the crow flies. The two points are connected by telegraph; and frequently when the Wetterleuchten, as seen from the Bel Alp, was in full play, I have telegraphed to the proprietor of the Monte Generoso Hotel and learned, in every instance, that our silent lightning co-existed in time with a thunderstorm more or less terrific in upper Italy.”[10] Another form of lightning, described by many writers, is called _globe_ lightning. It is said to appear as a ball of fire, about the size of a child’s head, or even larger, which moves for a time slowly about, and then, after the lapse of several seconds, explodes with a terrific noise, sending forth flashes of fire in all directions, which burn whatever they strike. Many accounts are on record of such phenomena; but they are derived, for the most part, from the evidence of persons who were not specially competent to observe, and to describe with precision, the facts that fell under their observation. Hence these accounts, while they are accepted by some, are rejected by others; and it seems to me, in the present state of the question, that the existence of globe lightning can hardly be regarded as a demonstrated fact. At all events, if phenomena of this kind have really occurred, I can only say that nothing we know about electricity, at present, will enable us to account for them.[11]