Historian Robert Righter and others have noted that the diameter of Charles Brush’s wind dynamo was 56 feet or about 17 meters in diameter.[1]
However, a question has arisen over whether this is accurate or not. The question arises from the famous photo of a man mowing the lawn near the windmill. If the man is ~1.7 meters tall is the rotor diameter 20 times the height of the man not 10 times?
I’ve found a passage in the 20 December 1990 issue of Scientific American where the diameter is mentioned. They write that the wheel is 56 feet in diameter or ~17 meters.[2]
“In the upper part of the tower is journaled the mainwheel shaft. This shaft is 20 feet long and 6-1/2 inches in diameter. It is provided with self-oiling boxes 26 inches long, and carries the main pulley, which has a diameter of 8 feet and a face of 32 inches. The wheel, which is 56 feet in diameter, is secured to the shaft and is provided with 144 blades, which are twisted like those of screw propellers.”
Scientific American 20 December 1890
The cover of that issue includes several sketches of the windmill and its key features. Using the measuring tool in Adobe’s pdf software, I measured the diameter of the rotor as ~7 inches, and the height of two men standing on the tower’s platform at ~0.7 inches or 1/10th the rotor diameter.
From these two sources it appears the historical record is correct that the Brush windmill was ~17 meters (56 feet) in diameter.
Applying the same technique to the famous photo of the Brush Dynamo in the possession of the Western Reserve Historical Society, the relative sizes are not as clear cut as in the Scientific American cover illustration. Nevertheless, the rotor appears ~10 times (4.5 inches) the size of the man mowing (0.33 inch).
[1] Robert Righter, Wind Energy in America: A History (Norman, Oklahoma: University of Oklahoma Press, 1996), and David A. Spera, “The Brush Wind Turbine Generator as Described in Scientific American,” in Wind Turbine Structural Dynamics, vol. DOE Publication CONF-771148, 19780011673 (Cleveland, Ohio, 1978), 275–83, https://ntrs.nasa.gov/citations/19780011673.
[2] “Mr. Brush’s Windmill Dynamo,” Scientific American, December 20, 1890, https://www.scientificamerican.com/article/mr-brushs-windmill-dynamo/, page 389.
