Under the French system, what is called in England a lightning conductor, and to which the French give the name _Paratonnerre_, is nominally divided into three parts: the terminal rod, the conductor, and the _racine_, or root, i.e. the earth connection. With regard to the terminal rod, the ‘area of protection’ theory is, in France at any rate, still believed in by a great many people. In that country, as a rule, it is made of wrought iron in a single length, and polygonal or slightly conical; its height depends upon the size and area of the building it protects, the general presumption being that, under ordinary circumstances, a terminal rod will protect effectually a cone of revolution, of which the apex is the point of the rod, and the radius of the base a distance equal to the height of the said rod above the ridge, multiplied by 1·75. Thus a rod rising eight yards above the ridge of a building would effectually protect a cone-shaped space, the base of which, at the level of the ridge, has a radius of 8 × 1·75 = 14 yards. In actual practice somewhat wider limits are allowed. The height of the terminal rod having been determined according to the circumstances under which it is erected, it is then galvanised with zinc in order to prevent oxidation, and the connection between the terminal rod and the conductor is formed by means of the following arrangement. A little above the base of the terminal rod, say about eight inches from the roof of the building, a flange A (see fig. 10) is welded with a hole pierced through it. Through this hole the conductor, previously filed down to the proper dimensions, must be tightly passed. After scraping the iron around the hole, a washer of lead is placed at P and P´ (see fig. 11), and the button B, by means of a strong layer of solder, thoroughly binds everything together. In this way an excellent joint is obtained; the contact surface is considerable, and, if the work is carefully done, the joint is completely preserved from rust. [Illustration: Fig. 12.] The point of the terminal rod, although sometimes made of platinum, generally consists of either pure red copper, or, what is considered still better, an alloy of 835 parts silver and 165 parts copper. It is fastened to the terminal rod in the manner shown in fig. 12. C is the trunk of a red copper cone, upon the top of which a point, P, made either of platinum or of an alloy of silver and copper, as before mentioned, is screwed, pinned, and strongly soldered with pewter solder at _a_, the whole being screwed on to T at _b_. To ensure complete contact and continuity, a washer of freshly-scraped lead is inserted between C and T, and the whole of the joint thickly covered with a layer of pewter solder. It may be added that the point forms an angle of fifteen degrees with the vertical, consequently the point terminates in an angle of thirty degrees. [Illustration: Fig. 13.]