Teltron Maltese Cross Tube. For demonstrating the straight propagation of electron beams in field-free spaces by projecting the shadow of Maltese cross on fluorescent screen. Also intended for observing the focusing of electron beams by magnetic fields as an introduction to electron optics. The lower section of the maltese cross has hole 3mm dia. which makes it possible to ascertain the orientation of the cross's shadow under the influence of magnetic fields.