The Moving Picture World (July 1907)

292 THE MOVING PICTURE WORLD. without being found out, is it not done? Contemptuous remarks about the littleness of the other firm and back- handed knocks are given when opportunity offers. And yet, the one can not do without the other; each firm has its own individuality, and, generally speaking, each uses the other firm's goods. Then why not drop the^ animus and join hands for the common good ? The field is large enough for all who are in, and for more who want to get in, so drop the dog in the manger policy, and join in a fraternal association for the common good, to drive out the pirate, and for future protection. It will be needed. Electricity for the Operator By H. Meredith- Jones, M. E., C. £. CHAPTER 3.— Continued. Tabus No. i. Comparative Standards of Wire Gauges. Dimensions of Wires in Decimal Part of an Inch. To measure wires by the above table the operaj should provide himself with a micrometer of at least half inch opening capacity; this size is a very useful ci it can be obtained put up in a neat leather case for an few dollars at a first-class hardware store. A microns as is generally well known consists of a knurled heaj screw for adjusting the jaws until they just touch j outside of the wire being measured and then reading] the number at the base of the screw as shown will ri the measurement in the number of thousandths of] inch. Each division equals an opening of the jawsj one thousandth part of an inch. There are also micron! ters made to read to a finer division of one ten-thousand part of an inch, but are used only by expert electrid who desire to read to another decimal point or figureJ Now, in using above table the different sizes are gj in decimals of an inch; the first number reading pastt! decimal point from left to right equals tenths of an ■ the next hundredths, the next thousandths, so you s you can easily and readily tell the size and gauge of )i wire in a very simple way. In cases where" two numbt in the same column read the same, for instance, like a and .004, then the upper one is a little thicker wire I another decimal point not shown, because the writer fa that three decimals is enough for all general practice. THE BROWN & SHARPE GAUGE. This gauge.is nearly universal in the United States! measuring wires and is referred to as a standard. Ill usually termed the B. & S. gauge. The sizes of n under the gauge range from No. 0000 (generally spot) of as four o), which has a diameter of .460 inch, nd half an inch, to No. 40, which has a diameter of .od inch; remember, the higher the number the smaller I wire. The rule by which the sizes of wire under I gauge increase as the number diminishes is a very simp one. For instance,' if we take any given number as basis of comparison, a wire three numbers higher i have very nearly half the cross section and one tha numbers lower twice the cross section. For exampl No. 4 wire has twice the cross section of a No. 7 vri and No. 10 has one-half the cross section of No. 7. Another point useful to bear in mind regarding ll B. & S. gauge is that a No. 10 wire has a diameter very nearly one-tenth of an inch, that one thousand J of this wire has a resistance of almost exactly one oh So by remembering this particular fact as well as 1 foregoing properties of this gauge, rough calculaufl can be made as to both the diameter and resistance other sizes. It is better, however, to consult the ta given for accuracy. Sizes smaller than No. 14, B. & S. gauge, are sel* used in electric transmission, but I have given a eoj plete table under Table No. 2 for reference, as the small sizes are largely used in connection with the windi? of various types of electrical apparatus, such as m^ small dynamos and motors, etc. Table II. gives the pro erties of copper wire according to the B. & S. gauge, a the resistances given are based upon the standard us by Matthiessen in his experiments; and if the purity the copper is not up to this standard, its resistance I run somewhat higher than the values given in the taa but the difference will not be so very great, becal copper wire, as now manufactured, is remarkably and uniform in character. All weights given are for bare copper wire.