Topic
- Nature 13
- Bridges--Design and construction 12
- Postcards 12
- Travel 11
- Water-power 11
- United States--Armed Forces--Organization--Charts, diagrams, etc 10
- Aerial photographs 9
- Bridges 9
- Dams 9
- Steamboats 8
- Agriculture 7
- Conservation of natural resources 7
- Forests and forestry 7
- Jetties 7
- Transportation 7
- Locks (Hydraulic engineering) 6
- Public utilities 6
- Railroads 6
- Roads--Design and construction 6
- Timber--Rafting 6