A light correction

February 2010, page 9

In Robert Crease’s interesting biographical discussion, “Charles Sanders Peirce and the First Absolute Measurement Standard” (Physics Today, December 2009, page 39), one small error crept in. As Leon Golub and I explain  in our book The Solar Corona (2nd ed., Cambridge University Press, 2009), spectroscopy was first used at  total solar eclipses in 1868 and 1869, with helium and what was at first called  coronium (now known to be a highly ionized state of iron) as the spectral  discoveries. Crease has checked his references and confirmed that the argon he  mentioned in his article was later reported by Peirce to have been observed not  at the 1869 eclipse in Kentucky but in an aurora at about the same time.

Jay M. Pasachoff

(jay.m.pasachoff@williams.edu)

Williams College

Williamstown, Massachusetts

A light correction

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