Face on dime before FDR

To answer the question from this article “Whose face used to be on the dime?”, I’ve found this claim on Wikipeadia’s article “Mercury dime”:

Where [23] = Burdette, Roger W. (2005). Renaissance of American Coinage, 1916–1921. Great Falls, Va.: Seneca Mill Press LLC. ISBN 978-0-9768986-0-3; page 172 …

But one way or t’other, it was Liberty, not Mercury. Nearly all US coins before 1909 had either Liberty or a generic “Indian”.

Why do they call them mercury dimes?
I have a vague remembrance of something to do with the element Mercury. Kinda like mercury glass.

NM.

The image is of Liberty wearing a winged cap. The image was confused with Mercury who also wore a winged cap.

And all this time I thought it was Golden Age Flash.

Duh! You would think I coulda figured that out!