Among the many interesting remarks of Dr. Holtz, evidently based on a thorough knowledge of the subject which he treats, are some good ones about the necessity of constructing lightning conductors, not slavishly after old models, but in conformity with modern requirements, carefully considering the nature of the buildings to be protected and their materials. ‘The increase of metals,’ he says, ‘in the construction of houses, both inside and outwardly, is assuming larger proportions from year to year. An absolute consequence of it is, that the electric force called lightning is tempted, far more than was the case in older dwellings, not to go to the conductor at all, or, if attracted to it, to leave the path afterwards, seeking other attractions. I found this to have been the case, in the course of my investigations, in several instances, two of them notable ones. The first was that of the public school of the town of Elmshorm, struck by lightning away from the conductor; and the second that of the church of St. Lawrence, in the town of Itzehoe, where the conductor was struck at first, but the lightning deviated subsequently from its metal path. In both cases I found that the non-efficacy of the conductor was caused by a number of gas-pipes. But there are many other metallic masses besides gas-pipes which interfere thus with the proper action of lightning conductors. More or less, all metals do so, especially those which lead to the ground, or are in contact with moisture. Water-pipes will attract the electric force even more than gas-pipes, and likewise the metal tubes which carry the rain from the roof into the ground. But it may also happen that mere ornaments on the roof, more particularly if of thick metal, and carried all along the top and sides, may divert the electric force from the conductor, although they have no connection whatever with the ground. Even the many wires outside and inside houses, for bells and other purposes, may do mischief. There can be no doubt whatever that the large increase of the use of metals in the construction and ornamentation of modern houses has led to far greater danger to which they are exposed from lightning. At the same time there is equally little doubt that all this increased danger may be absolutely guarded against by the setting up of lightning conductors by competent persons, carefully designed to meet all cases.’ Dr. Holtz adds, further on, that one most important element of protection to be obtained from conductors consists in the regular testing of them, without which, indeed, there can be no permanent security.