The magnitude of the K{sup 0}{sub S} - K{sup 0}{sub L} mass difference has been measured by monitoring the time dependence of the strangeness of neutral K's produced in hydrogen and deuterium in the LRL 25 '' hydrogen bubble chamber. The particles originate as K-bar{sup 0} in K{sup -} change-exchange scatters at .85 to 1.15 Bev/c; the signature for an S = -1 reaction is the production of a hyperon. Seventy- seven events were found, obtaining {Delta}{omega} = 0.50 =- 0.15, measured in units of inverse K{sup 0}{sub S} lifetime. This and two other recent measurements using the same method are consistent with one another and with measurements of {Delta}{omega} by other means. A combined ''world average'' of nine reasonably consistent measurements gives {Delta}{omega} = 0.60 +- 0.06.

A double-focusing magnetic field for a spectrometer of the flat type which gives radial focusing to roughly the sixth order, and which utilizes azimuthal variation of the field coefficients, has been devised.