576,202. Safety shutters. DONALDSON, F. G. April 26, 1944, No. 7789. [Class 20 (iii)] [Also in Group XXI] A safety shutter for a projection room or other aperture is held by the direct action of an electro-magnet in the open position and allowed to fall under its own weight when the magnet is de-magnetised. In the arrangement shown in fig. 1, in which two shutters are connected by a pivoted lever 6, the heavier shutter 1 is held open by an armature 4 secured to it and bridging the poles of an electro-magnet 8 secured above the shutter frame. The current through the magnet is controlled by push button 13 or automatically by a tilting mercury switch 14, Fig. 4. mounted above the projector gate. A piece of film or other inflammable material attached to the sliding member 16 holds the spring 17 compressed and the switch in the closed circuit position. In a modification the switch, which is preferably situated near the film gate, is of ordinary type and thermally operated. In a further modification the switch is remote from the fusible material and controlled by Bowden wire mechanism or the like.