Why does the image seem to move in the opposite direction to the way the slide was moved using a microscope?

You know how when you are using a microscope to view a particular specimen, and you're not satisfied with the sells that you see in that particular space in the slide, you tend to move the slide slowly and gently. But the thing I want to know is why when you move the slide a little to the left, the image you see in the microscope moves right, and again the other way around. Anybody?