Perot's number is now definitely adopted to define the Angstrom, and need never be altered, for should at some future time further researches reveal a minute error, it will be only necessary to change slightly the temperature or pressure of the air in which the wave-length is measured.
Jacques Perot thanked the treasurer for her scrupulous work on behalf of all members of the Executive Council.
Some other appliance in which interference with long difference of path is made use of, such as the interferometer of Fabry and Perot, or Lummer's plate (see Interference Of Light) .
For the study of Zeeman effects (see Magneto-Optics) the echelon seems specially adapted, while the great pliability of 'Fabry and Perot's methods, allowing a clear interpretation of results, is likely to secure them permanently an established place in measurements of precision.
Jacques Perot thanked the Treasurer for her scrupulous work on behalf of all members of the Executive Council.