The beta-spectra of ${\mathrm{S}}^{35}$ and ${}_{61}{}^{}{}_{}{}^{}\mathrm{Pm}_{}^{147}{}_{}{}^{}$ have been measured in order to study further the nature of any low energy deviation from the Fermi theory of beta-decay. Measurements were made with thin, relatively uniform sources in both the 40-cm radius of curvature spectrometer and also in a small 180 degree focusing Helmholtz coil spectrometer designed specifically for low energy spectra. The thinnest sources were less than 10 micrograms/${\mathrm{cm}}^2$. Using Zapon counter windows ranging from 15 to 3 micrograms/${\mathrm{cm}}^2$ and also a windowless counter technique, Fermi plots were obtained which showed how the measured distribution of particles at low energy depends on both source and counter window thickness.

Favorable experimental conditions yielded a straight line Fermi plot for ${\mathrm{Pm}}^{147}$ above 8 kev. Less favorable conditions resulted in a straight line plot for ${\mathrm{S}}^{35}$ down to at least 50 kev. Thus, ${\mathrm{S}}^{35}$, which is allowed, and ${\mathrm{Pm}}^{147}$, which is probably once forbidden, are found to have spectra of the allowed shape. It is concluded that under very favorable experimental conditions there is probably no real disagreement between the observed momentum distribution and that predicted for an allowed transition by the Fermi theory. On the basis of an improved calibration, the following end points are obtained: ${\mathrm{Pm}}^{147}$, 223.2±0.5 kev and ${\mathrm{S}}^{35}$, 167.0±0.5 kev.

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