for numbers which appear in the middle of each block. Print from the zinc plate a number of strips of blocks. With shears and a paste-*pot, another vertical row of blocks may be added at the right-hand edge of the chart copy each month to provide "copy" for the plate to print the succeeding month's illustration. The identification could be lettered by hand inside of the vertical row of blocks for the latest month. It then takes only a short time to draw lines joining blocks having corresponding numbers. The built-up "copy" is then ready for the engraver to make a zinc plate. Zinc plates cost so little that there is almost negligible expense required for the new line cut needed each month.
In Fig. 64 the general scheme of Fig. 63 is expanded so that the chart shows not only the rank, but also the comparative size of the units under consideration. This illustration shows also some interesting combinations of shading by means of which blocks of distinctly different appearance are obtained. Fig. 64 was photographed directly from a United States Government report. Otherwise, the years would not be shown here reading from right to left instead of from left to right. Though the right-to-left arrangement is unfortunate, the general scheme of Fig. 64 is excellent, as it gives a large amount of information in a small space. The convenience due to this method of double comparisons, either horizontal or vertical, gives it a decided advantage in clearness.
Train charts like that shown in Fig. 65 are very commonly used by railroads, rapid-transit subways, etc. Fig. 65 would not look so complex if colored ink were available to show in contrast the express passenger trains, the work trains, etc. It is suggested that the reader observe the key at the top of Fig. 65 and then follow a few of the various trains from one end of the line to the other, taking into consideration the fact that this is a single-track railroad and that trains must pass at the turnouts which are available. To schedule a passenger train such as that leaving Tyrone at 12:25 p. m. is no simple proposition on such a crowded railroad as this.
In rapid-transit work in large cities a time-distance chart in the general scheme of Fig. 65 is almost essential if methods of giving high-speed service to the people are to be studied. These time-distance charts can be made on so large a scale that two horizontal lines may be used to indicate the stations, with the lines spaced a distance apart to show to scale the actual length of each station platform. Time-
