FIG. 1 is a perspective view of a bubble machine in accordance with our design;

FIG. 2 is a side elevation view thereof, the opposite view being a mirror image of that shown;

FIG. 3 is a front elevation view thereof;

FIG. 4 is a back elevation view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom plan view thereof.

The broken lines are included for the purpose of illustrating portions of the bubble machine that form no part of the claimed design.