Motion Picture Herald (Jan-Feb 1936)

any conducting material it will induce a voltage in that material, therefore current will tend to flow in or through it. This is sometimes referred to as inducing a voltage or current in the material, for the current is not brought there by any electrical connection, but is induced by a magnetic field. A "squirrel cage" induction motor has a rotating element, usually termed the "rotor," which has conducting material laid in slots around its cylindrical surface. This conducting material may be bars of copper, aluminum or any other suitable material. These bars are connected to end rings. A variation employed is insulated copper coils connected to slip rings. In either case the magnetic field set up by the current flowing through the stator windings rotates so that it cuts the conductors of the rotor, thus inducing voltage and causing current to flow through them. Now whenever a conductor carrying current is placed in a magnetic field, there is a force caused to act against the conductor, which tends to cause it to move through the said field. In the case of an induction motor a field has been set up by connecting the line voltage to the stator winding. A current has thus been caused to flow through the rotor conductors by the voltage induced in them by the stator current. Now this current must of course flow through the magnetic field set up by the stator. As a result of all this there is a force tending to move the rotor conductors, which, since the rotor conductors are located in slots in the rotor itself, must cause the rotor itself to move and it is this force that gives power to induction motors. MORE PROTECTION AGAINST PITTING MANUFACTURERS of light sources using reflectors have, in their newer equipments, adopted pretty generally a shield designed to protect the reflector from incandescent carbon particles when the arc is struck. It is in the form of a piece, usually of some heat resisting metallic composition, attached to a conveniently located handle by means of which it may be lowered between reflector and positive crater before the arc is struck, and raised out of the way when its purpose has been accomplished. It is good, so far as it goes, but there lies the trouble. It doesn't go far enough. Reflectors now in use are rather costly bits of equipment. They may now be had with a positive guarantee for six months, save only so far as has to do with pitting. The shields now in use protect the top and center of the mirror from pitting, but not their lower outer portion. I have myself examined reflectors pretty badly pitted at these points, notwithstanding the fact that the shield was, the projectionists averred, always used when striking the arc. The point I am getting at is just this: The shields as now used help a lot. That is admitted. But I am unable to see any reasonable reason why they could not be so made that they would protect the entire mirror surface. So far as that is con High Intensity Lamp Buy quality! It Is Wisest, Eventually Understanding experience, advanced design and creative engineering have earned for Peerless their traditional reputation of superiority. The Peerless Magnarc is the only low voltage high intensity lamp that is the same today as it was when first put on the market and yet Peerless is still far advanced in design. If you did not purchase Peerless Magnarcs — what are your orphan lamps worth now? Answer this question fairly and you have undeniable proof that — Real economy lies not in a low first cost or can be had in any other lamp. DISTRIBUTED BY NATIONAL THEATRE SUPPLY CO MFD. BY J. E. McAULEY MFG. CO. 552-54 W. ADAMS STREET CHICAGO, ILL. January 11, 1936 31