Page:Graphic methods for presenting facts (1914).djvu/323

 Fig. 218. Reflectoscope as Made by A. T. Thompson & Co., Boston, Mass.

Lantern slides may be used as shown at the top of the picture. The stand holding the book may be replaced by a simple carriage arranged to take the 4-by-6-inch and the 4-by-12-inch curve cards. The very latest data from the file shown in Fig. 217 may then be instantly reflected onto a screen for use in a meeting of the department heads of a business.

lantern slides each time a new point is plotted on each curve would be too great for even the largest corporations. Another disadvantage of using lantern slides is the impossibility of getting slides made quickly enough to represent always the latest points plotted on the curves. By using the original curve cards directly in the reflecting lantern there is always a certainty that the picture shown on the screen represents the very latest data which are available in curve form. When these curve cards are used in a reflecting lantern a simple slide carriage is made to replace the stand holding the book in Fig. 218. As the card is laid down flat in its natural position and in plain view of the operator, there is no likelihood of cards being put into the machine incorrectly. If a carriage about two feet long is used, the carriage may be moved alternately from right to left, and while one side contains the cards which are being reflected on the screen, the other side may be loaded with the cards next desired. On account of its length the carriage will hold curve cards for several succeeding years. By pushing the carriage slowly across the lantern the fluctuation in any curve may be shown for as long a series of years as may be desired. Simple spring clips on the carriage may be used to hold the overlapping cards in their
 * ings of department heads must be held. The expense of making