The eight conductors descend the length of the octagon of the spire until they reach the first gallery; going round this they pass over the balustrade, and then converge towards each other; are carried over a prominence in the roof; and as they pass along gather up other conductors of similar size from the ridges and parapets of the buildings which form the quadrangle. Projecting vertically from these horizontal lengths of the conductors are a large number of points and aigrettes. The summits of the lower tower are also furnished with a great many points. These eight main conductors are then taken down the wall of the building into the courtyard, and at about three feet from the ground are carried into a box constructed of galvanised iron, and in it are connected into one solid mass by zinc, which has been poured molten into the box. Almost throughout their length the conductors are left loose, so as to remove all complication arising from dilatation; the play of this dilatation being rendered easy on account of the small section of the conductors, which bend readily. In accounts of lightning striking buildings which have been provided with lightning-conductors, it is almost invariably found that these conductors are incomplete, and have generally been fixed by persons ignorant of the scientific questions involved. When the facts in such cases are carefully examined it is found, as a rule, that the defect is in the connection with the water underground, or in the bad conductivity of the earth in which the conductors terminate. In establishing a perfect communication with the earth, M. Melsens considers it is necessary, not only to place the conductors in contact with water, but also to see that the contact extends over a large surface. The Paris Academy ‘Instruction’ recommends this precaution, but in a very vague and too succinct a manner. To the above rule may be added another condition, namely, that the earth-connection should be large in proportion as the site of the building is redundant in metal products in direct or indirect contact with the ground, the subsoil, or the damp earth of the foundations, and sometimes even with water itself. With regard to the metal contained in the materials of buildings, it is not sufficient to establish a connection at one point only, as is generally supposed. On the contrary, it is important that all the metal-work should be connected with the conductor at least at two points, in order to realise closed metallic circuits, and thus offer an entry and exit, or a free metallic course, for the current of electricity. The foregoing statements have been placed here chiefly because the principles they convey have been so rigidly, and at the same time successfully, carried out by Professor Melsens at the Hôtel de Ville, Brussels. [Illustration: Fig. 3.]