68 



THE EFFECTS OF LIGHTNING. 



Dresden, and are still preserved there. Nearly a century elapsed before they 

 were seen again, when, in 1805, Dr. Hentzen found them in Paderhorn, com- 

 monly called La Senne. This philosopher first assigned their origin. They 

 have been since found in great numbers at Pillau, near Konigsberg ; at 

 Nietleben, near Halle upon Saale ; at Drigg, in Cumberland ; in the sandy 

 country at the foot of Regenstein, near Blankeriburg ; and in the sands of Ba- 

 hia, in Brazil. 



At Drigg the fulgurites are found in hillocks of moveable sand, about forty 

 feet high, close to the sea. At La Senne they are usually discovered at the 

 brow of hills of sand about the same height ; sometimes also in a cavity, form- 

 ed like a basin, one hundred feet in circumference, and fifteen feet deep. 



Fulgurites are usually hollow tubes. At Drigg their diameter is generally 

 two and one fourth inches. Those at La Senne vary from one fiftieth of an inch 

 to half an inch in diameter, and contract as they descend, terminating frequent- 

 ly in a point. The thickness of their sides varies from the fiftieth of an inch 

 to an inch. These tubes usually descend -in the vertical direction, being occa- 

 sionally, however, inclined at an angle of 40 to the horizon. Their total 

 length sometimes amounts to above thirty feet. Numerous transversal fissures 

 divide them into fragments, the lengths of which vary from half an inch to six 

 inches. The sand by which they are surrounded dries and falls off after a lapse 

 of time, and these fragments are then seen on the surface of the ground, the 

 sport of the wind. 



Most commonly, in clearing away the surrounding sand, the fulgurite is found 

 to consist of a single tube. On following it to a certain depth, this is divided 

 into two or three branches, each of which again divides into small lateral rami- 

 fications, varying from one inch to twelve inches in length. These final rami- 

 fications are conical, and terminate in points, which are gradually inclined 

 downward. 



The interior surface of the tubes is coated with a perfect and very brilliant 

 glass, resembling vitreous opale, or hyalite. It cuts glass and strikes fire with 

 steel. Whatever be the form of these tubes, they are always surrounded by a 

 crust composed of grains of quartz agglutinated together. This crust is some- 

 times round ; it is oftenest like the bark of a stump of an old birch-tree. The 

 interior and exterior surfaces correspond in form, as if the .tube were soft and 

 flexible, and acquired hardness after being bent. 



When examined with a microscope, the exterior crust presents marks of fu- 

 sion. At a certain distance from the centre of the tube the grains or globules 

 acquire a reddish tint. The color of the material of the tube, and especially of 

 the exterior parts, depends on the nature of the sandy soil in which it has been 

 formed. In the superior strata, which consists of common soil, the exterior of 

 the tube is usually black ; deeper, it is a yellowish gray ; and deeper still, a 

 grayish white. Finally, where the sand is pure and white, the tube exhibits 

 nearly perfect whiteness. 



Such being the appearances presented by fulgurites, the question is present- 

 ed : Whence do they originate, and by what natural process have they been 

 formed? Four hypotheses were proposed to explain them: 1. They might 

 have been incrustations formed round roots, which disappeared after the opera- 

 tion ; 2. They might be stalactites or other mineral formations ; 3. They might 

 be cells belonging to ancient marine animals of the worm species ; 4. They 

 might be produced by lightning penetrating the ground. 



The first three of these hypotheses include, as a necessary condition, the 

 formation of the fulgurites at an epoch more or less remote from the present 

 time. If it can be shown, then, that, whatever be their origin, it must, in some 

 cases at least, be recent, these hypotheses must be severally rejected. The 



