The Faraday Effect in Gases and Vapors. I

Using a newly developed photoelectric method that will measure magneto-optic rotations as small as 0.0003°, Verdet constants have been measured for helium, neon, hydrogen, deuterium, nitrogen, oxygen, and butane. This has been done at gas pressures less than 3 atmospheres for 22 points over the spectral range λ3635 A to λ9875 A. The average probable error is estimated at slightly less than 1 percent. Interference filters, calibrated specially for this type of work, have been used to give reasonably monochromatic wavelengths with a resulting uncertainty for most of the spectrum of not more than 10 A. Where comparison is possible with the work of other observers the agreement is satisfactory. The Faraday dispersion for helium follows closely the inverse-wavelength-squared law. Other gases are roughly similar, save oxygen which is anomalous. The Verdet constants for all gases show a negligible temperature dependence, at constant density, and for all gases except butane show negligible pressure effects for the moderate pressures used.