The effects of lightning are so various that it would take a book to describe them all. Its audible effects are discussed in our chapter on atmospheric acoustics. Its chemical effects consist chiefly in the production of oxides of nitrogen, ozone, and probably ammonia from the constituents of the atmosphere along the path of the discharge, and these substances, either directly or after further combinations in the atmosphere, contribute to the fertility of the soil. Lightning sometimes bores holes several feet deep in sandy ground and fuses the material along its path, forming the glassy tubes known as _fulgurites_. Similar holes are bored in solid rock. The destructive effects of lightning are due chiefly to the heat generated by the passage of an electric current through a poor conductor. When moisture is present in the object struck, its sudden conversion into steam produces the explosive effects seen in the shattering of trees, the ripping of clothes from the human body, etc. There is almost no end to the curious pranks played by lightning--some disastrous, some comical, and some benevolent, as when persons crippled with rheumatism, after having been knocked down and temporarily stunned by a stroke of lightning, have found themselves completely cured of their malady! A well-known book by Camille Flammarion, translated into English under the title “Thunder and Lightning,” is almost wholly devoted to these eccentricities of the lightning stroke. [Illustration: A LIGHTNING PRINT ON THE ARM OF A BOY STRUCK BY LIGHTNING NEAR DUNS, SCOTLAND, IN 1883 _Drawn from a photograph taken a few hours after the accident__. From the Lancet._] There is a very common belief that lightning sometimes impresses a photographic image of trees or other objects of the landscape upon the human body. The ramifying pink marks, known as “lightning prints,” often found on the skin of persons who have been struck by lightning, are, however, in no sense photographic, but are merely the lesions due to the passage through the tissues of a branching electric discharge. A few practical suggestions in regard to danger from lightning are offered by Humphreys, as follows: