The handbook of kinematography, the history, theory, and practice of motion photography and projection (1911)

Record Details:

Something wrong or inaccurate about this page? Let us Know!

Thanks for helping us continually improve the quality of the Lantern search engine for all of our users! We have millions of scanned pages, so user reports are incredibly helpful for us to identify places where we can improve and update the metadata.

Please describe the issue below, and click "Submit" to send your comments to our team! If you'd prefer, you can also send us an email to mhdl@commarts.wisc.edu with your comments.




We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.

Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.

160 HANDBOOK OF KINE MA TOGRAPH Y. Electro-magnetic machines specially adapted to give power in the shape of rotation in response to feeding with electric current are termed ' motors/ Small motors of one-eighth horse power or less are now commonly used in the operating box to turn the mechanism of the projector, instead of the operator doing it by hand. These small motors consume little more current than an ordinary sixteen candle carbon filament lamp. Now to turn to electrical nomenclature. DIRECT AND ALTERNATING CURRENT (D.C. AND A.C.) The electric ' current/ as it is termed (the word is not in any sense explanatory, and an attempt to give here the modern theory as to what electricity actually is would be productive of no practical good) this electric ' current' is generated of two kinds, direct and alternating. Direct current flows in a constant stream from the positive to the negative pole of the generating system, and that is all there is to say about it, but alternating current may be looked upon as a succession of electrical waves going in opposite directions. Each wave pulses through the circuit in an almost infinitely short space of time, dies down, and is succeeded in the fractional part of a second, by another one going contrarywise to the last. Thus, with the alternating kind of electricity there is really no positive and no negative pole, since both terminals of the generator become alternately positive and nega- tive at intervals of anywhere between the twenty-fifth and the one hundredth part of a second. The sum of alternations of direction of current flow per second is spoken of as the ' periodicity ' or number of ' cycles ' of the alternator producing it. Thus, a fifty cycle system would be produced by a fifty cycle alternator. All this means that with the particular description of alternating current in use, the direc- tion of flow alters fifty times in each direction with each second of time. Note that whereas either direct or alternating current may be produced by an electrical generator according to the system of ' commutation/ or current collection employed, storage battery systems give only direct current. Also, systems involving auxiliary storage batteries for use in case of temporary breakdown of machinery are invariably of the direct current type. In stamping the descriptive plates to be affixed on electrical machinery, and otherwise in the notation of electrical energy, a straight line stands to denote direct and a curved one, alternating current. In kinematograph projection, employ direct current whenever possible. It is more economical than alternating when used for the projection arc. Further, the arc's crater, on which it will subsequently be found the performance of the arc depends, is formed much more satisfactorily and is much steadier when direct than when alternating current is employed. Also, where the kinematograph is to be