When certain bodies, such as leather belting and pulleys, paper and steel plates, or cotton and steel rolls, are rubbed together, sparks are frequently produced. This kind of electricity is called frictional or static, and is quite dangerous because of its liability to cause a fire. Frictional electricity acts in many ways like magnetism. To illustrate: A magnetized body has at least two poles which are unlike and the magnetism appears more or less concentrated. In like manner, when a body which is rubbed becomes electrified, it shows two different kinds of electricity. For instance, if a sheet of glazed paper is rubbed vigorously with a smooth pencil and then placed over a small piece of paper, the sheet attracts the small piece, showing that the bit of paper has a different electrification from that of the sheet. When two different substances are rubbed or passed over one another quickly, one becomes charged positively with electricity, while the other is negatively or oppositely charged.