Other observers, besides, have declared that they saw distinctly the spiral lightning flash through the atmosphere. But these observations would need to be confirmed by photographs of indisputable accuracy. In these circumstances, as in many others, the dark room is worth a hundred human eyes!
In some cases the curved furrow turns several times. For instance, in May, 1850, Grebel saw an alder nearly twenty metres high struck by lightning on the right bank of the Elster below Zeitz. On the lower part of its trunk were two spiral bands which had carried away bark and sap-wood, leaving no trace of combustion.
The depth and width of the twist are very variable; at times the furrow is deeper in the veined parts than at the edges; again it reaches the core.
Two oaks were struck in June, 1742, in the park at Thornden. One was marked with a spiral for a length of forty feet to within a little distance of the ground. The band was five inches wide, but became narrower as it descended, and was finally no more than two inches wide. The wood was incised and even torn in places, but the branches were not hurt. The rest of the bark seemed to have been riddled by small shot.
All the injuries of which we have spoken (excoriation, stripping off the bark, furrows), are not necessarily mortal. But there are other more serious wounds from which the tree rarely recovers. We allude to deep fissures and breaks produced by lightning. When the fracture touches only a portion of the topmost part of the tree, the result of the accident is not necessarily fatal. But this is not always so.
On May 14, 1865, a poplar was split in two by lightning at Montigny-sur-Loing. One half to the full height continued standing. The other half was chopped up in small fragments and thrown to a distance of a hundred metres. These pieces, which were brought to me by M. Fouché, are so dried up and fibrous that they might be taken for hemp instead of wood.
In the majority of these cases the tree is split from top to bottom.
On July 5, 1884, in Belgium, a poplar, the biggest of a group of trees of the same species, was struck and split down its full length.
In the month of August, 1853, on the side of the road from Ville-d'Avray to Versailles, a poplar of about twenty years old was cleft from the topmost bough to its roots; one half remained in its place, the other fell on the road. A black line, about a millimetre wide, ran down the centre of the tree.
Sometimes the tree is divided into several parts by vertical fissures. For example, in 1827, near Vicence, a pear tree, three feet in diameter, was split into four parts, from the top down.