| O | |
|---|---|
| O'Callaghan | Vol.6.No.2.Page 5 |
| O'Hara, Michael | Vol.6.No.1.Page 10 |
| Ojibwa Indian Mission | Vol.5.No.1.Page 4 |
| Oil Reservoir windmill | Vol.6.No.2.Page 6 |
| Old Reliable Freeport windmill | - see - Freeport Machine Co. |
| Vol.7.No.4.Page 9 | |
| Old Reliable Stover windmill | Vol.7.No.4.Pages 9 (illus), 10 (illus) |
| - see - Stover Wind Engine Company | |
| Oliver | Vol.3.No.2.Page 4 |
| Oppenheimer & Co | Vol.2.No.1.Page 9 |
| Vol.2.No.2.Page 2 | |
| Vol.4.No.1.Page 2 | |
| Oregon wood | Vol.5.No.4.Page 11 |
| Original Monitor Vaneless windmill | - see - Baker Original Monitor Vaneless windmill |
| Osbourne, Joseph | Vol.9.No.3.Page 5 |
| Osborne, W. F. | Vol.6.No.1.Page 6 |
| Vol.9.No.3.Pages 1, 5 (illus), 7 | |
| Osbourne, William Frederick | Vol.9.No.3.Page 5 (illus), 6 |
| Osbourne, William Frederick (senior) | Vol.9.No.3.Page 5 |
| Osbourne windmill | Vol.9.No.3.Page 5 |
| Outwood Mill (UK) | Vol.7.No.4.Page 2 (illus) |
| Overall McCray Ltd | Vol.6.No.1.Page 4 |
| Owen, Joel D. | Vol.7.No.4.Page 6 |
| Owens College (UK) | Vol.8.No.2.Page 2 |
| Ozark Pump Co | Vol.6.No.1.Page 7 |