How can I scroll using my middle mouse button?

A scroll wheel is a hard plastic or rubbery disc on a computer mouse that is perpendicular to the mouse surface. It is normally located between the left and right mouse buttons. It is used, as the name suggests, for scrolling. It can also be used as a third mouse button by pressing on it. Some newer mice can be used to scroll horizontally as well as vertically, using either a tilting scroll-wheel (introduced by Microsoft) or a scroll ball (found on Apple's Mighty Mouse). In many operating systems, holding down the control key and using the scroll wheel causes the text size to increase or decrease, or an image in an image-editing program to zoom in or out if such a feature is available in the editing program.