The ornamental design for a microscope, as shown and described.
FIG. 1 is a top, front perspective view of a microscope;
FIG. 2 is a front view thereof;
FIG. 3 is a back view thereof;
FIG. 4 is a left-side view thereof;
FIG. 5 is a right-side view thereof; and,
FIG. 6 is a top view thereof.
The broken lines depict portions of the microscope that form no part of the claimed design. The bottom view is omitted as forming no part of the claimed design.