The device used to compare the relative magnitudes of charges on two given bodies is a gold leaf electroscope. A gold leaf electroscope consists of two thin gold leaves that are attached to a metal rod inside a glass or plastic enclosure. When a charged object is brought near the metal rod, it induces a charge on the leaves. The leaves, being like charges, repel each other and spread apart. By observing the degree to which the leaves separate, you can compare the relative magnitudes of charges on different bodies. This makes a gold leaf electroscope a valuable tool for demonstrating the presence and relative strength of electric charges.