We claim the ornamental design for a portion of an electron microscope, as shown and described.
FIG. 1 is a front, top and right side perspective view of a portion of an electron microscope showing our new design;
FIG. 2 is a front elevational view thereof; the rear view is not part of the claimed design;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a front, top and right side perspective view thereof shown in an opened positioned; the front, top and left side perspective view of the claimed design (shown in solid lines) is a mirror image of the claimed design as shown in FIG. 8.
The broken lines shown are for illustrative purpose and form no part of the claimed design.