It was not, however, until the Bath meeting of the British Asso ciation in 1888 that the subject was fully discussed by the physi cal and engineering sections.
Sir Oliver Lodge showed the futility of single conductors, and advised the interconnection of all the metal work on a building to a number of conductors buried in the earth. The action of lightning flashes was also demonstrated by him in lectures delivered before the Society of Arts (1888). The Clerk Max well system was adopted to a large extent in Germany, and in July 1901 a sub-committee of the Berlin Electrotechnical Association was formed, which published rules. In 1900 a paper entitled "The Protection of Public Buildings from Lightning," by Killingworth Hedges, led to the formation, by the Royal In stitute of British Architects and the Surveyors' Institution, of the Lightning Research Committee, on which the Royal Society and the Meteorological Society were represented. The Report, edited by Sir Oliver Lodge, Sir John Gavey and Killingworth Hedges, was published in April 1905. An illustrated supplement, compiled by K. Hedges and entitled Modern Lightning Conductors, contains particulars of the independent reports of the German committee, the Dutch Academy of Science, and the Royal Joseph university, Budapest. A description is also given of the author's modified Clerk Maxwell system, in which the metal work of the roofs of a building forms the upper part, the rain-water pipes taking the place of the usual lightning-rods.
A number of failures of conductors were noticed in the 1905 report of the Lightning Research Committee. One cause was the insufficient number of conductors and earth connections; another was the absence of any system for connecting the metallic por tion of the buildings to the conductors. In some cases the main stroke was received, but damage occurred by side-flash to isolated parts of the roof. There were several examples of large metallic surfaces being charged with electricity, the greater part of which was safely discharged, but enough followed unauthorized paths, such as a speaking-tube or electric bell wires, to cause damage. In one instance a flash struck the building at two points simul taneously; one portion followed the conductor, but the other went to earth jumping from a small finial to a greenhouse 3o ft. below. (Photographs and specimens showing such damage are exhibited in gallery 44, Geophysics, of the Science Museum, London.) Construction of Conductors.—The general conclusions of the Lightning Research Committee agree with the independent reports of similar investigators in Germany, Hungary and Holland. The following is a summary of the suggestions made : "The conductors may be of copper, or of soft iron protected by galvanizing or coated with lead. A number of paths to earth must be provided; well-jointed rain-water pipes may be utilized." Every chimney stack or other prominence should have an air terminal. Conductors should run in the most direct manner from air to earth, and be kept away from the walls by holdfasts (fig. ), in the manner shown by A (fig. 2) ; the usual method is seen in B (fig. 2), where the tape follows the contour of the building and causes side flash. A building with a long roof should also be fitted with a horizontal conductor along the ridge, and to this aigrettes (fig. 3) should be
attached ; a simpler method is to support the cable by holdfasts armed with a spike (fig. 4). Joints must be held together mechan ically as well as electrically, and should be protected from the action of the air. At Westminster Abbey the cables are spliced and inserted in a box which is filled with lead run in when molten.