The Moving Picture World (June 1907)

ig6 THE MOVING PICTURE WORLD. 1 Electricity for the Operator. By H. Meredith-Jones, M. E., C. E. Preface. The electrical knowledge of most operators of the cinematograph or magic lantern is limited, in most cases to simply knowing how to connect up? his own especial form or type of machine properly, adjust his carbons in his lamp, and regulate the current by means of-his resist- ance coils or rehostat. It is the intention of the writer of these series of articles to make clear as well as simple the so-called mysteries of that ever absorbing topic "Electricity," to show the operator the why and wherefore of it all. How electricity is measured, man- ufactured and transmitted to the user. It'is the desire of the writer to be as concise as possible, consistent with the requisite amount of explanation, to make the subject of electricity a more easily understood one in popular language. Chapters. No., i The Forms of Electricity. No. 2. Electrical Measurements. No. 3. Wires, Conductors and Wiring Tables. No. 4. Direct .Current Generation. No. 5. -Alternating Current Generation. No. 6. Alternating and Direct Current Transformers. No. 7. Electric Lamps. Incandescent and Arc. No. 8. Electric Motors. No. 9. Electric Heaters. Rules of National Board of Underwriters. Dictionary of Terms. Tests and Testing Apparatus.' _ Chapter No. i. THE FORMS OF ELECTRICITY. Electricity is at present ah unknown substance so far as its exact nature is concerned, that is as to what elec- tricity realiy consists of, such as we know, for instance, of water, clay, coal and other kindred substances. We know definitely its various forms, such as static, frictional, voltaic, direct, alternating, etc, but it will only be in connection with the two latter that I shall write, as they are those which are so well known and only come directly in the field-of the operator's every-day work, as they are the only ones- now supplied by all light, heat and power companies to the daily users of electric current, or "juice," as most operators call the electrical energy. Although we do not know definitely, as I have just stated, what electricity exactly is, we do know how to produce it, measure it, use it, control it and even weigh it. These various methods will be fully explained in their respective chapters in such a manner as to meet the entire needs of the cinematograph or magic lantern operator, and in these chapters I shall only treat with sufficient of the subject under its caption to make the operator thoroughly conversant with, and able to handle any proposition -be may meet with in his lifetime. The obscure and trie unnecessary are omitted, as they concern only the electrical engineer or the student. Before passing to the two main forms of electrical energy as supplied and used everywhere to-day, viz., the direct current, familiarly known as the D. C, and the alternating current, fanriliariy known as the A- C-, let us pause Iof a moment and study the close analogy or sim- ilarity between the flow of an electric current through a conductor or wire to the flow of water through P'pe. You all know, of course, that water to flow through pipe must have a pressure behind it to overcome the re- sistance of the pipe, so exactly does an electric current need a pressure behind it to force it through and to overcome the resistance of the conductors or wires and to perform certain work in any fona of apparatus. By referring to the following diagram which will show more clearly what is meant by the fore- going remarks and will well illustrate the similarity be. 1 &. tween them. In Fig. 1 let A represent the source of sup ply either of water or some like liquid. Now as there sistance of the pipe retards the flow the pressure will dro and therefore less water will flow, so in Fig. 1. I dj a ! grammatically show by .means of upright tubes branching from the main pipe and by the height of a column of water in each tube show the amount of water tfe would be supported by the pressure at that givo point which results from loss of pressure clue to th friction or resistance within the pipe, so it is with eke tricity, the pressure drops in direct relation to the it sistance to be overcome, as, for instance: In Fig. 2, B rep resents some source . of electrical energy, such as i dynamo, generator,, switchboard, or panel, with two cos ductors or wires branching therefrom with lamps plat* in parallel between the wires or conductors, as in plan of the columns of water in Fig. 1. Now the nearest to B will burn the brightest since it is nean the source of energy. supply and the one at the a| treme end will burn the dimmest because the pressu will have been weakened by the resistance of the ca ductor or wire, as its distance is greater from its son of supply than it is in the case of the first la Although in general practice it is usual to all conductors and wires of a size large enoiij to prevent any serious loss of pressure so that all Ian would burn uniformly in brightness, but this subject ti| be treated more fully under chapter No. 3, on wires, cor ductors and wiring tables, but suffice it to remember, f" like water, electricity falls in pressure or potential (>j sometimes referred to) in a direct relation or proporf " to the resistance to be overcome and that the current^ likewise affected and altered in quantity in direct pro tion to the above two named factors as, for instance, resistance being constant and uniform, you increase yo pressure more current will flow, or if the pressure J constant and you decrease your resistance more cur" will flow, and thereby is constituted a well-kno* electrical law, known as "Ohni's Law," which positively the simplest as well as the most fun mental law or principle upon which any science ever based and is unchangeable tender all conditions !