> >(you'd not considered a little motor to do the rocking ?). > > Ah, now that brings back memories of doing the PSSC Physics > course at secondary school. Large flat water tanks with motor and > eccentric weight to make waves in the water ... Blinds down, light bulbs, diffraction gratings ? -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist