LIST OF PLATES 



FIGUBE 



ii. The Dodge instrument for training gun-pointers Frontispiece 



FACING 

 PAGE 



1. Uniform rate of ascent of pilot balloon up to 11,000 



meters . . /. . .... . . . . 5 



2. Pilot balloon ascent showing isolated convection current 51 



3. Uniform rate of ascent of pilot balloon up to 20,000 



meters where balloon sprung a leak. . .... 54 



4. Convection currents at low altitudes . ... . . 55 



1. Example of airplane photograph. Trenches, concrete 



dug-outs and machine gun emplacements along the 

 Yser River N . . . . . . 94 



2. The method of building up a mosaic map from a large 



number of overlapping serial photographs ... -94 



3. Color filters in aerial photography . . ... V . 95 



2. Portable army telephone exchange . . . . - . . . 228 



3. Portable 4-line switchboard . . . 228 



4. Portable outpost switchboard 229 



5. Signalers in gas masks talking with observer in a captive 



balloon ........ t. . \ .... 229 



6. Brigadier-General Edgar G. Russel, the Chief Signal Of- 



ficer of the A. E. F .' *..... 236 



7. Major-General Squier, Chief Signal Officer, U. S. Army 236 



8. Types of vacuum tube . . . ...... . . . . 237 



9. Airplane radiogenerator 237 



10. Interior parts of radiogenerator ........ 237 



1. A trade test in the United States Army . . . . . 354 



2. An individual psychological examination in the United 



States Army 355 



3. Testing the mechanical skill of soldiers by the Stenquist 



method V . > 358 



4. Examination Alpha . :... . , . . . . . . . . 359 



Group of soldiers at Camp Lee, Virginia, taking the army 



psychological examination for literates. This was be- 

 fore benches were provided in the examining room ! 



Soldiers scoring psychological examination papers 



xix 



