"In the accompanying cuts are shown the distinctive features of a double filament incandescent lamp that has been recently introduced in the English market. The arrangement is such that when one filament is exhausted, the other may be used. Reference to the cuts will make the details clear. In Fig. 1, the middle wire, Y, is attached to one of the contact plates, C, in the usual manner, and the outer wire, X, is attached to the contact plate, D. The other outer wire, Z, is attached to another contact plate, E, which is placed immediately under the plate, D, but insulated from it by a very thin layer or membrane of non-conducting material. On the lamp being put in the circuit the current entering by the contact plate, E, and issuing by C, or conversely, causes only the one filament, B, to become incandescent, but when B is worn out, the plate, E, can be raised and the insulating material between the two plates, D and E, being withdrawn and scraped away, the plate, D, which had been previously insulated is now brought into the circuit, and thus the other filament, A, is rendered incandescent. In like manner, when more than two filaments are placed in the bulb, their leading in wires are connected to separate contact plates, each insulated from the other, so that each in its turn can be put in circuit by removing or scraping away the insulating material from between it and the contact plate for the filament previously used. As shown in Fig. 2 the middle wire, Y, is connected by a cross wire, G, to the socket, H, the wires, X and Z, being respectively connected to two contact plates, D and E, thin insulating material being placed between them as in the first instance, which is easily removed when one of the filaments is worn out, the other being immediately brought into the circuit. The latter arrangement is especially applicable for lamps used in series as instead of short-circuiting and thus cutting a lamp out, the high potential current penetrates the thin insulating membrane and causes another filament to become incandescent. The cuts are reproduced from the London Electrical Review."