# Circle is Bisected by Diameter/Historical Note

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## Historical Note on Circle is Bisected by Diameter

The result that a Circle is Bisected by Diameter was supposedly attributed to Thales of Miletus by Proclus Lycaeus.

Euclid defines the diameter as the line which passes through the center, but then assumes that it necessarily bisects it:

*A***diameter of the circle**is any straight line drawn through the center and terminated in both directions by the circumference of the circle, and such a straight line also bisects the center.

According to Julian Lowell Coolidge in his *A History of Geometrical Methods*:

*It seems strange that Thales, a disciple of the Egyptians, should bother to demonstrate something which Euclid takes as self-evident. Proclus suggests that he proved it by folding the circle over the diameter.*

## Sources

- 1992: George F. Simmons:
*Calculus Gems*... (previous) ... (next): Chapter $\text {A}.1$: Thales (ca. $\text {625}$ – $\text {547}$ B.C.)