The ornamental design for a microscope, as shown and described.
FIG. 1 is a perspective view of a microscope, showing may new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top plan view thereof; and
FIG. 7 is a bottom view thereof; where those illustrated by broken lines forms no part of the claimed design; and,
FIG. 8 is another perspective view of the microscope viewing from a lower side thereof; where those illustrated by broken lines forms no part of the claimed design.