Motion Picture News (Mar-Apr 1923)

March 10, 1923 1207 Simplified Electricity for Projectionists {Continued Ironi page 1206. the south pole ami ^o through the magnet to the north pole (Fig. 4). It is these lines of force which exercise the effect of attracting or repelling bodies as the case may be. Thus if two north poles are brought near each other, since the lines in each case are leaving the north poles, they will buck each other and hence push the two poles away. In the case of two south poles, however, the lines are both going in the same direction leaving the north pole and entering the south pole so the two poles will he attracted. The reason why certain demagnetized pieces of metal are attracted to the north or south pole, as the case may be, is explained as follows: If a piece of soft iron, for example, is brought near the north pole of a magnet, it will be magnetized as explained before and lines of force will now from the first magnet to the nearest end of the soft iron and induce or set up in it a new south pole. The opposite end will become a north pole. As unlike poles attract each other the soft iron is drawn to the magnet. The process is reversed in ease the soft iron is brought near a south pole. The action of inducing a pole in an iron bar is as follows : Fig 5 shows the lines of force coming out of the north pole of a permanent magnet. Now it is a fact that the air offers a greater resistance to these lines than does the iron. Since the iron offers aa easier path to the lines from the magnet, more of them will be drawn to it. Hence the lines will Send in Your Questions on these Articles crowd into this end of the iron bar, and since the condition for a south pole is that the lines of force must enter it (Fig. 4) a new pole is created which is a south one. The opposite end of the bar must then become a north pole since there can be only one north and one south pole in any given magnet at the same time. If the first magnet should be removed from the soft iron bar it (the bar) will immediately lose its magnetism. F iff it re 5 Dear Sir: Although I am not what one might call a professional projectionist, yet I have operated machines of various makes since my sixth grade in grammar school. We are having a show a week here and as we are having a great deal of trouble, due to misframes, bad mending and the like, I am tendering my application to join the League. I realize that the pledge contains very concisely the film evils and I willingly take it and resolve to do my best to correct these faults and to always send away a film in better condition than I re ceive it. Enclosed please find 25 cents in stamps for button, and please send me membership card and shipping blanks. Let me know of any charge. Thanking you for your kindness, John E. O'Beien, Georgetown Prep. School. Garrett Park, Md. GUNDLACH dNDlAo PROJECTION #> LENSES . Sold lubject to mppromal by all Jaalar*. Writ* today for it lamtrated folder. PROJECTION LENS An Improved projection lens for beat film projection. Unsurpassed Luminosity — Increased Efficiency — Adaptability to Mazda as well as arc light source— Brilliancy of Image — Clear cut definition. PBICB8 a. 1 Bis* Proj e o t I o n Lenses without jackets.. $11.00 No. 1 8 1 a • jackets S.M No. 2 Size Proj e c t 1 o a Lenses without jackets.. 9SO.00 No. 2 Size Jackets 5.08 Gundlach-Manhattan Optical Co. 853 Clinton Avenue South Rochester, N. Y. H. ROBINS BURROUGHS M. All. SOC. C B. THEATRE ENGINEERS Plant and Specifications Assistance in Financing 70 EAST 45th STREET NEW YORK Information o r advice concerning equipment for the Theatre is furnished gratis by the Technical Department of the Motion Picture News. PROJECTION MACHINES OVERHAULED AND REPAIRED Simplex, Powers, Monograph, Edison and all other makes. Best equipped machine shop; expert mechanics. We can repair your old machine and make it as good as new. Prompt Service Reasonable Prices Expert Work Note: — To get the best and most satisfactory service from your projection machines, have them overhauled at least once every two years. MOVIE SUPPLY COMPANY 844 S. Wabash Avenue Chicago, Illinois NO MATTER WHAT THE FEATURE A marquee is a permanent drawing-card for your theatre. Choose from our large selection or send sketch or photo and we will design one specially for you. ProBert SHEETMETALCO. CINCINNATI, OHIO