The Bioscope (Jul-Sep 1931)

IV THE BIOSCOPE MODERN CINEMA TECHNIQUE August 19, 1931 ARC CONTROL POSITIVE ( Continued from CARBONS page iii) through in order to lubricate the walls of the hole. It might be noted here that in a 12 millimetre positive the diameter of the core hole is 21 millimetres. Everything being now in readiness, the core paste is hydraulically squirted through and is allowed to flow out of the end of the shell momentarily before being stopped off. This process is illustrated in the view at Figure III. It now remains to solidify and harden the core throughout before the carbon passes to the final stages of testing, labelling and packing, and this is effected by a short oven treatment at 100 deg. C. in order to ensure that the shell and its core form one consistent whole. Electrical Characteristics The mirror positive which may have a diameter of between 8 and 14 millimetres and a length of 8 or 9 inches is now a finished product, and we can lay it aside and pass on to a consideration of the negative which is to form its opposite number. Finally, when considering low intensity crater formation we shall revert to the subject of the positive and it will be shown how the various processes touched upon above have each of them a bearing upon some aspect or another of the arc the quality of which governs the success of the picture to be shown. For the moment it will serve to bear in mind that our mirror positive consists now from an electrical point of view of two resistances in parallel : A low one — the shell — of pure hard carbon, and a higher one — the core — of comparatively soft material. The cross sectional areas of these two resistances are roughly proportional to those of the lead and the wood in an ordinary pencil, and the proportions in which the current divides itself through these two parallel resistances is a factor of great importance to the satisfactory working of the arc. Of this anon. Coles Plans Broadstairs Super Broadstairs, the Kentish coast resort, is to have a new cinema. At the present time there is one cinema, a repertory theatre and two concert parties in the town A site has been obtained in York Street, one of the most prominent thoroughfares in the town, and plans have been passed by Broadstairs and St. Peter’s Urban District Council. The plans have been prepared by George Coles, F.R.I.B.A., and the promoter of the scheme is Harry Fowler, of Providence House, Granville Road, Broadstairs. It is, as yet, undecided which type of " talkie ” apparatus to instal in the new building, which has been designed to accommodate 1,100 people. It is hoped to open the new cinema next spring and tenders for its construction will be invited in the autumn. Some Points for Ever since the sound film made the perforated screen an essential there has been a constantly growing demand for more light, and many projectionists have attempted to supply this by increasing the arc amperage. In a good many instances either by the use of additional power — where this has been available — from the generator, or by the use of special carbons, projectionists have been successful ; but more amperage has frequently meant more breakages. Larger amperage means a larger arc flame and the larger arc flame has frequently got near enough to the mirror to cause trouble. It has been suggested that the projectionist can get away from this trouble by building for himself a magnetic flame control. With luck, he can. A Simple Electro-Magnet All that is needed is a U-shaped soft iron band so that one arm of the U rises on each side of the arc. This band must be mounted on an insulating base, to prevent electrical contact with either the arc lamp itself or with the base of the lamp house. Everyone who has had any personal contact with Film Industries, Ltd., knows that the company is very largely indebted on its research side to Douglas T. Bennett, the clever son of the company’s very able managing director. Bennett, Jr., has a very welcome tendency to break away from the c o n v e n tional line in research work, and this has been particularly useful in developing the F.I. set. We have already paid tribute in these pages to the excellence of the company’s loud speaker, which has been described by a rival manufacturer as the best on the market without exception. Praise of this kind is not gained easily. the Projectionist The positive lead to the arc is then wound f uir or five times round one arm of the U before the current is fed to the positive carbon. In fact, the U-shaped iron arm is turned into an electro-magnet controlled by the arc current. Quite Simple — If Care is Taken This is very simple in theory, but in practice the snag lies in the well-known fact that the number of turns round the arms affects the strength of the magnet. Too few turns will not have any effect ; too many — and the arc may frequently put itself out ! The proj ectionist may be fortunate in building one of these for himself, but he is equally likely to run his head into a whole lot of trouble. The magnetic control working properly is most excellent, but an inefficient one is fatal. If you cannot induce the theatre to supply you with mirror arcs in which the magnetic control is supplied by the makers, it might be just as well to ask your accessory dealer to supply you with a reliable control before you risk experiments which can prove expensive. Bennett, Jr., spent three years studying electrical engineering at City and Guilds College. At the time when “ The Singing Fool ” was running in London he ran the first Dutch ” talkie ” in Holland on the first set installed at The Hague. Prior to concentrating on reproduction he had experimented for two years on recording. Young Bennett has personally carried out several theatre installations and is thoroughly sound, practically as well as theoretically. In fact, he holds that no job can be carried out with complete success unless both theoretical and practical aspects are grasped. Patents Taken Out He has recently been concentrating on two fields — reproduction of sound and neon light research. In this latter field he has taken out several patents, having developed a new type of tube in which the glow can be made to spread through the tube at will. As far as reproduction is concerned, he has produced several interesting speakers and amplifiers. A public address van, capable of delivering intelligible speech at a distance of two miles, has also been designed by him. In fact, Film Industries’ technical director is a thoroughly sound man both in theory and practice. A “Sound” Engineer Film Industries’ Technical Director r rr #-r * i c-_. . SHIP “ HILO ” CARBONS are recommended by us, and can be supplied either from our Head Office at 94, Wardour Street, London, W.l, Gerrard 5137, or from any of our Branches below. Birmingham, Cardiff, Glasgow, Leeds, Manchester. Newcastle. 1 • «