Hemmer not only wrote a number of little books, which he liberally distributed, but travelled about through many parts of Germany, instigating the authorities to place conductors on all public buildings, and the people to set them up over their own houses. Holding that the earth connection was everything, he advocated simply to dig a hole in the ground till water or very moist earth was reached, and to stick a small iron bar, wrapped in lead to prevent rust, into it, running up the roof. The bar any village blacksmith could forge, and the hole any man or boy could dig, thus making the absolute cost of the conductor under this arrangement very trifling. Dr. Hemmer was right, no doubt, in his main argument, and most successful in spreading the knowledge of lightning conductors, while he was able to boast that not one of all the number he had set up had ever failed. However, he lived in an age when as yet water and gas pipes were unknown, and iron, or any other metal, scarcely entered into the construction of buildings. Given a leaden roof and a network of metal tubes, and Dr. Hemmer’s small iron rod could scarcely be expected to do its work of protection. Together with Dr. Hemmer in Germany, Professor Landriani, of Milan, drew attention to the paramount importance of a perfect earth connection. He made it his special business to investigate cases in which buildings with lightning conductors had been struck, and was able to show in nearly every instance that it had been for want of ‘good earth.’ A very striking case, which ought to have brought conviction of the truth to all investigators of the subject, occurred in Genoa in 1779. The church of St. Mary in this city, standing in a very elevated position, had been frequently struck by lightning, sometimes as often as twice in one year, and it was noticed that the electric force always followed precisely the same path, running along a certain portion of masonry, partly secured by iron hoops, and finally demolishing a wall at the bottom to get into the earth. At last, in November 1778, a conductor, made of the most approved design, was placed over the church, but, to the great surprise of the scientific men who had superintended the work, the lightning fell once more upon the building in the month of July of the following year, again following the old path it had constantly taken before, and causing absolutely the same damage as previously, even to the knocking out of certain portions of the wall nearest the ground. Naturally, the event caused widespread interest, leading to the closest examination of the church of St. Mary by several experts, among them Professor Landriani. He had no great trouble in discovering both the causes of the path of the lightning having always been the same when falling upon the church, and of the edifice having been struck again in the same manner when provided with a lightning conductor. Being a somewhat peculiar structure, consisting