Page:Popular Science Monthly Volume 20.djvu/677

Rh  have secured specimens of them for their collections. It is hard to get large ones, and they command a high price. At first, their true nature was misapprehended. They were regarded successively as incrustations formed around roots that had disappeared; as the cells constructed by worms of extinct species; and as a kind of stalactites. Hentzen seems to have been the first one who attributed them to lightning;

 Tubes produced by the vitrification of sand by the passage of lightning through the soil in the deserts of Poland. (From a specimen in the Museum; figure one third the natural size.

and his opinion has been shown to be correct by Blumenbach and by Tiegler. More recently, Nature has been caught in the act; that is, fulgurites have been found in sand which was still hot, at the spot where the lightning had been seen to strike. Besides, several experimenters, as Beudant, Huchette, and Savart, have obtained tubes analogous to fulgurites by discharging the great electrical battery of the Conservatoire des Arts et Metiers through beds of pounded glass, or of sand mixed with sea-salt to make it more fusible. Fulminated tubes are found principally in places where beds of sand lie upon a soil which contains water, and is consequently a conductor of electricity; for example, at certain points in Silesia, in Eastern Prussia, Poland, Cumberland, and Brazil.



HE extremes between which the duration of the lives of plants varies are widely removed from each other. On one side, we may see plants that begin and close their lives within a few hours or days; on the other side, plants, the lives of which may be estimated 