Whiting's notes on induction-coil size.

The article "Sarah Frances Whiting and the "photography of the invisible" ( I Physics Today i , August 2020, page 26) was fascinating. I offer a different interpretation of Whiting's notes on an x-ray photography experiment that was "executed with a 6 in. coil" - the induction coil used to supply high voltage to the Crookes tube that produced the x rays. In the nomenclature of the day, the maximum voltage of an induction coil was measured in inches, referring to the maximum length of air-discharge spark it could make, the most reliable way to measure high voltage at the time. [Extracted from the article]