An analysis of certain heads of the sequence $v^{\prime }-v^{\prime \prime }=+1({}_{}{}^2{}_{}{}^{}\Sigma \to {}_{}{}^2{}_{}{}^{}\Sigma )$ in SrF arc emission spectra, revealed three components at each of the first heads, the displacements of which show the presence of three strontium isotopes at masses 88, 87, and 86. A quantitative determination of the abundance ratio, 88/86 gave a value of 8.52, which is in reasonably good agreement (+2.0 percent) with the abudance ratio of 8.38 determined mass spectrographically. The accuracy with which this ratio has been determined is considered to be within ±4-6 percent. Abudance ratios, 88/87 and 87/86 could be determined only approximately because of masking of the ${\mathrm{Sr}}^{87}$F component by the dominant ${\mathrm{Sr}}^{88}$F component. The spectra had been recorded using first order (dispersion, 0.848 A/mm), but if second order were used, this masking would be reduced to an insignificant amount. For geological age requirements, mass-spectrographic measurement of strontium isotope abundance ratios is preferable because as little as 0.3 mg of strontium salt is required, whereas using molecular spectra, far larger amounts are required. As the maximum concentration of strontium in the most ancient rubidium-rich minerals does not exceed 0.02 percent, inconveniently large quantities of mineral have to be employed to extract sufficient strontium for a molecular spectroscopic analysis.

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