They should first look for materials suitable for making filaments. Among the tested metals, platinum (also called platinum) seems to be the most ideal one, because this material meets the requirements of high resistance and slow heat dissipation. On October 5th, 65438/kloc-0, Edison filed a patent application for platinum wire "electric lamp". The filament of this bulb is a double helix made of platinum wire, and a metal rod is added between them. When the heat of the filament is close to the melting point of platinum wire, the metal rod will expand and cause short circuit, and the temperature of the bulb will decrease. When the platinum wire cools, the metal rod will also cool down, so the current will pass again. However, platinum is expensive, which is not conducive to popularization. Soon, Edison gave up using platinum wire and switched to platinum foil, but success always seemed so far away.