Illinois Central Railroad, 310 Illusions, optical, 358, 359 Imports and exports of United States, 37 Incandescent-lamp tests, 337 Income curves, 197 Income of technical graduates, 204 Increases shown graphically, 30 Independent, the, 21, 38 Independent variable, definition, 84 Index numbers, 100 Indianapolis Department of Health, 114 Indianapolis smoke deposits, 245 Industrial depressions, 104 Industrial Engineering, 117, 118 Infectious diseases shown in contrast, 30 Information cards, 286, 290

Ink, drawing, 46, 47, 276 Internationale Baufach-Ausstellung, 225 Inversely related curves, 126 Inverted curves, 96 Iron Age, the, 110, 119 Irregular curves, use of, 201 Isometric drawings, 333 ruling, 167, 334, 335

Japanese road signs, 346 Jersey Cattle Club, American, 278 Jevons, Stanley, 319

Joint Board of Sanitary Control, 166, 253 Joint Committee on Standards for Graphic Presentation, ii, 363

Keufi'el and Esser Company, 326 Key for charts, 360 King, Willford I., ii, 328

Labeling packages, 90, 91 Lamps, types in use, 138

tests of incandescent, 337 Land value in United States, 218 Lantern slides for election returns, 341

slides in political campaigns, 339

talks in political campaigns, 340 Legend for charts, 360 ,

Lenses, camera, 330

cylindrical, 330 "Less than" basis for frequency curves, 179 Lettering on charts, 26, 82 Letters of appeal for money, 250

gummed, 46 , •

Lighter operation, chart for, 56 Line cuts from pin maps, 234

made from green ink, 330, 331 Line thickness in reduced drawings, 242 Lines connecting different bars, 31 Loans to industrial employees, 156 Locomotive feed-water curves, 159 Logarithmic co-ordinates, 132

paper, 334, 362