With the exception of the terminal rod, it is the rule in France to cover the whole of the paratonnerre with some coating in order to preserve it from contact with the air. This is attained by covering it with either a strong coat of tar, or a painting of a metallic basis, such as zinc or tin filings. [Illustration: Fig. 15.] In larger buildings what is termed a ‘ridge-circuit’ is often used. It consists of an unbroken metallic connection running along the ridges of the building to be protected, and connected with the conductors and terminal rods, and consequently with the subterraneous sheet of water which forms the common reservoir. It is made of lengths of square iron bars or rods having a thickness of about three quarters of an inch square, and fastened together by overlaying the ends, bolting them together with two bolts, and covering them well with solder in the manner shown in fig. 13. New branches are formed by T-shaped connections, the cross-piece of the T overlaying the original ridge-circuit, and the stem making the first length of the new branch. In some cases the ridge-circuit rests directly on the ridge of the roof; but in order to avoid injury during the repairs to the roof or in other ways, the plan adopted in good work is to raise it some distance above the ridge on supports at suitable distances, and thus prevent the possibility of damaging the joints and solderings. The form and arrangement of these supports depend on the nature of the roof. Sometimes forked uprights are used--these allow for the expansion and contraction due to changes of temperature; in other cases simple cast-iron bearings, weighing from ten to twelve pounds each, are laid upon the ridge, their upper surfaces being grooved to receive the bars of the ridge-circuit. All masses of metal used in the construction of the building are metallically connected with the paratonnerre. As a rule, this is done by pieces of iron about half an inch square, which are strongly soldered to the metal surfaces, and then connected with some part of the conductor or ridge-circuit. Although in France, as elsewhere, all experts are agreed as to the prime importance of the disposition and arrangement of the _racine_ or earth-end of the paratonnerre, a difference of opinion prevails as to the best means of insuring a good earth-contact, and many methods have been tried, all of them similar in principle, but differing somewhat in application. It is proposed to give here a brief outline of the best contrivances employed for this purpose.