Moving Picture World (Mar-Dec 1907)

244 THE MOVING PICTURE WORLD. Electricity for the Operator By H. Meredith Jones, M. E. , C. E. Continued from Page 229 THE UNITS OF MEASUREMENT. THE UNITS OF LIGHT. All light of any kind whatsoever is measured by the term or name of candle-power. This arose from the fact that the earliest known form of satisfactory lighting was a candle. By comparing the light to a common candle its power was known or determined; for instance, a 16candle-power lamp is supposed to equal sixteen unit candles. Now, as candles were a very changeable quantity in light-giving power, according to its composition and weight, it was decided to determine upon some legal standards, and the “Paris Congress” decided upon the legal standard of light as follows : The unit of each simple light is the quantity of light of the same kind emitted in the normal direction by a square centimetre of the surface of molten platinum at the temperature of solidification. The practical unit of white light is the quantity of light emitted normally by the same source. A square foot of surface is equally illuminated by a standard candle, at a distance of 12.7 inches, and a 16candle-power lamp at 4 feet 2 inches gives the same illumination. The British unit of candle-power is the one generally used and accepted ; it is near enough for all practical purposes, although they sometimes may vary as much as 10 per cent, from the standard. It is the amount of light of a pure spermaceti wax candle seven-eighths of an inch in diameter, burning 120 grains per hour; six candles weight one pounds. The French and German units are only given here simply to give the operator a knowledge of them in case he happens to run across them by chance during his travels around the world. The French unit of light, or Bec-Carcel, is the light of a carcel lamp, burning 42 grammes of pure colzra od per hour with a flame 40 millimetres high, under conditions fixed by J. B. Dumas & Regnault. It is taken to equal 9.5 British standard candles, and, of course, is gy2 times more powerful. The Ferman unit is the light of a paraffin wax candle 20 millimetres in diameter, burning with a flame 5 centimetres high. The Bec-Carcel is taken to equal 7.6 German candles PFIOTOMETRY. The measurement of light, or photometry, as it is called, may be very interesting to all operators, and T will explain a very simple and sufficiently accurate method of testing light values. There are many ways known to science for testing light values, all of which are not suit able for a work of this character on account of their complication and methods involved which are very exact, but the following method is sufficient for the purposes and needs of an operator, as well as simple, cheap and fairly accurate. The light to be measured must be compared by means of a standard candle as above ; first buy a pure spermaceti wax candle; insert this in a candlestick or holder of any kind ; next make a white screen about two feet square, of white paper — or use your lantern screen, for instance ; next get a stick or round rod and place near the screen in an upright position (a foot away from the screen) ; now light your candle and place it behind the upright rod — a little to the right of the rod and behind it — so that it casts a shadow of the rod upon the screen ; then place on the left, behind the rod, the light to be tested, which will cast another shadow of the rod upon the screen bv the side of the shadow cast by the candle. Now move the light to be tested away from the screen until the two shadows are exactly alike in appearance, then measure the distance from the screen to the light being tested, and also from the screen to the candle. Now multiply each distance by itself and divide one into the other, which will give the candle-power of the light being tested. For example, say the candle is two feet from the screen and the light being tested twelve feet from the screen. Then, multiplying two feet by itself (two feet) we have four, and multiplying twelve feet by itself (twelve feet) we have one hundred and forty-four; now dividing four into one hundred and forty-four we get thirty-six candlepower as the answer. Remember, the number of times the lesser divides into the greater — after each has been multiplied by itself as shown above — is the number of candle-power of the light being tested. (To be continued.) POSING FOR SONG PICTURES.— In response to one advertisement recently printed calling for “handsome young men to pose for pictures” there appeared young men to the number of five. Of these two could not have been by any stretch of the imagination considered handsome. The other three were well dressed and, generally speaking, slightly appearing young men though one of them was far enough from handsome to put him out of consideration, while of the other two neither was really handsome, though what with their other favoring qualifications both would answer for the purposes required. And so out of a bunch of five young men there were found just two who, though not coming up to the highest standard, would do. What they were wanted for was to pose for pictures to be reproduced on lantern slides to be used on the stage with illustrated songs. For an illustrated song there are usually required seventeen slides. As to its words, the song is likely to consist of two verses, with a chorus repeated after^each verse, thus giving the song as sung four sections. One of the lantern slides used with the song shows a reproduction of the title page of its sheet music, and this picture is first thrown on the screen ; and then as the singer sings it the pictures in illustration of the words are shown. Most of the illustrated songs are love songs, and so of the men required for the illustration of such songs the greater number must be young. It is easy to say what would be the ideal requirements of a man who would make a complete satisfactory picture of a lover. He must be of good , stature, any wav, and then he would need to be of good figure and bearing, a fine, manly, courageous young man, and withal handsome. As such a combination is tolerably hard to find in one young man, the lantern slide people have more or less difficulty in finding really suitable subjects. In search of them they advertise in the newspapers, and have recourse to theatrical agencies, where they may find actors