Moving Picture World (Jan-Feb 1927)

462 MOVING PICTURE WORLD February 5, 1927 Bluebook School Answers 552 , 553, and 554 Note: — This “School” is designed to arouse interest in the study of those many problems which constantly arise in motion picture projection, AND to cause men to really study the Bluebook and assimilate the vast amount of knowledge contained within its covers. Question No. 552 — Why should the rheostat, as a whole, be insulated from earth? In addition to those already named, George Lawrence, Jr., Sackville, New Brunswick; Frank Dudiak, Fairmont, W. Va. ; E. Fergodo, Livermore, Calif. ; Harry Spada, Woodlawn, Pa., and A1 Lehman, Glenside, Pa., replied acceptably. All replies were much alike. John Doe answered a bit the most fully. He said : If the rheostat be connected into the neutral of an Edison 3-wire circuit it would not matter whether it were grounded from earth or not. Under any other condition, however, if the rheostat as a whole be not thoroughly insulated from earth, and the live part became grounded to the frame, so that the frame became itself electrically alive, then there would probably be current leakage, which might be slight, or be heavy enough to blow a fuse. In any event it would be a waste of electrical energy so long as the condition continued. Question No. 553 — What is the objection to using ordinary iron wire for resistance purposes? There were not many replies to this, probably because it was thought of small importance, but while that is true, perhaps, still it was asked to see whether or no you really understand the effect of the temperature co-effiient, and that it varies hugely in different metals. George Lawrence, Jr., projectionist, Imperial Theatre, Sackville, N. B. ; E. Fergodo, Livermore, Cal., F. D. Orenbacher, Truesdale, Mo.; Frank Dudiak, Fairmont, W. Va. : W. C. Budge, Springfield Gardens, N. Y. ; John and “Bill” Doe, Chicago, 111.; Gilbert Atkindon, Cleveland, Ohio, and Allan Gengenbeck, New Oreans, La., answered correctly. Brother Fergodo says: Ordinary iron w ire has a very high temperature co-efficient, which means that its resistance varies largely with changes in its temperature. If it were used for the resistance element in a rheostat for projection work, then since the rheostat would have to be so constructed that it would deliver the amperage required for the work when its resistance element had reached its working temperature, it would mean that until that temperature was reached it would deliver excess current flow, and when the arc was first “struck” and the resistance cold, the excess would be very heavy. “Bill” Doe puts the matter in very simple form, thus : Ordinary iron wire has much less resistance when cold than when hot, hence is not suitable for rheostat resistance. Put in technical language it has a very high temperature co-efficient, which means that the resistance varies largely with temperature changes. It therefore is unsuitable for resistance purposes. Question No. 554 — Name the chief objections to iron grid rheostats. Brother Lawrence says : The chief objections are: (A) They are much heavier than wire coil rheostats of equal capacity, hence more difficult to handle and more expensive to ship. (B). It is a greater task to replace a damaged grid that it is to replace a wire coal. (C). The temperature co-efficient of cast iron is lower and more variable than that of resistance wire, hence the amperage regulation as between the cold and hot grid is not so close as between the hot and cold resistance coil. (D). A heavy jar is more apt to injure a cast grid rheostat than a wire coil one, because the grids are more or less brittle, especially after extended use.” Reflector Arc Lamp (Continued from preceding page) DOES IT NOT APPEAL TO YOU AS JUST COMMON SENSE THAT IT WILL BE WELL FOR YOUR MANAGER TO SELECT YOUR REFLECTOR TYPE ARC EQUIPMENT FROM THOSE WHICH HAVE HAD THE CONFIDENCE OF THEIR MAKERS OR SPONSORS TO THE EXTENT THAT THEY HAVE SUBMITTED THEM TO THE INSPECTION OF THE EDITOR OF THIS DEPARTMENT???? I know nothing about the Gardner Reflector Arc Lamp equipment. ' I have carefully examined the Peerless, the Powerlite, the Strong and the Hallberg Lamp. Each of these is strictly high-class equipment which I can recommend to you. Each of these will have full, detailed instructions for its operation in the new Bluebook. I do not say there are no other good reflector type arc lamps, mark you, but I DO SAY THAT IT IS A BIT FOOLISH TO PURCHASE EQUIPMENT CONCERNING THE EXCELLENCE OF WHICH YOU CAN ONLY JUDGE BY MEANS OF YOUR OWN UNTRAINED EXAMINATION AND THE BEGUILING TALK OF INTERESTED PARTIES— THOSE WHO HAVE THE GOODS FOR SALE. That is, after all, the big point. In this department you get absolutely disinterested advice from a man whom no one has ever yet, in seventeen long years, accused of practicing deception concerning equipment, regardless of advertising or other considerations. You say you prefer a Peerless or a Powerlite. Well, then your manager will do well to install one of them. They are both strictly^ high-class equipment. As to joining the union, you seem to be about ten miles nearer Macon than Atlanta, therefore are, under I. A. law, in the jurisdiction of Macon. The secretary of the Macon local is R. A. Godfrey, Box 451, Macon, Ga. It is a “mixed” local— stage hands and projectionists. You might write brother Godfrey asking whether or no you would be welcomed by the local, provided you can meet their requirements. I cannot say that you probably would derive any immediate benefits from membership, but you would at least have the satisfaction of knowing you are doing your duty. If you ever should leave Washington, membership doubtless would be an advantage. As to a license, no. The only one you could get would be a city license, I think, and there is no object in that unless you expect to work in the city you get the license from. Regarding your having had more “hours of experience,” my friend Truitt, it is most emphatically NOT the number of hours you have or have not worked that counts, provided they have been sufficient to thoroughly acquaint you with projection apparatus and procedure, but the use you have put the hours to. The man who merely learns to “operate a machine” may work for many years and still be almost totally ignorant of those things which go to make the real motion picture projectionist. And that last is not mere idle talk either, mind you. The machine operator learns to operate the machine and then stops. To him the only thing that counts thereafter is quitting time and pay day. Optical action and any more electrics than knowing how to find a blown fuse or what to do when a wire gets so hot the insulation smokes is “junk.” It is not so long ago that I knew of the examination committee of a very large union actually testing the ability of a projectionist by tearing a projector mechanism to pieces and seeing whether or no the candidate could reassemble it, which merely showed the utter, total lack of conception of the problems of projection possessed by that committee. A more idiotic thing could hardly be imagined, because ability to reassemble that mechanism satisfied the committee, while failure condemned the applicant, and that was that. I hope and believe most unions have gotten past that stage by now. You seem to be studying. Keep it up ! The trouble might lie right here : The Macon union presumably operates under a wage scale which applies to, and doubtless is just and right for Macon, but which might not be just or right for your little town. The local might or might not insist on you getting the scale. Probably not. but you should have an understanding on that point before joining, if the union is willing to accept you. It is the sole arbiter on that last point. For Your Library The J. E. Macauley Mfg. Co., 552 West Adams street, Chicago, 111., will send you, for the asking, a copy of their excellent illustrated booklet in which their “Peerless” reflector type arc lamp and equipment is described. Projectionists should have such things as this on file. Send and get it. Good stunt. The New Edition of F. H. RICHARDSON’S HANDBOOK OF PROJECTION H as Been Delayed In Printing Announcement of the Date of Its Appearance Will Be Made Very Soon CHALMERS PUBLISHING COMPANY 516 Fifth Avenue NEW YORK CITY