Probably by using wavelengths of monochromatic cadmium red light in normal air at 15º C. Similar experiments were carried out on the metre as early as 1892. All the preparatory work using various monochromatic lights between 1892 & 1940 resulted in the adoption of the 1650763·73 orange-red Krypton wavelength definition of the metre in 1960
--- On Mon, 6/4/09, Jeremiah MacGregor <[email protected]> wrote: From: Jeremiah MacGregor <[email protected]> Subject: [USMA:44433] Re: The_inch_is_no_cinch!_=97_formerly_= Re: Even with "dual," you can't please everybody To: "U.S. Metric Association" <[email protected]> Cc: "U.S. Metric Association" <[email protected]> Date: Monday, 6 April, 2009, 3:49 AM I'd like to know how they were able to measure the yard to 8 decimal places way back in 1893. What instrument did they use Jerry
