High-field measurements on the high-$T_c$ superconductors ${\mathrm{La}}_{1.85}{\mathrm{Sr}}_{0.15}\mathrm{Cu}{\mathrm{O}}_{4-\delta }$ and $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$

We have measured the superconductive properties of the high-$T_c$ superconductors ${\mathrm{La}}_{1.85}{\mathrm{Sr}}_{0.15}\mathrm{Cu}{\mathrm{O}}_{4-\delta }$ and $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ in magnetic fields up to 25 T. Conservative estimates of the critical field at $T=0\mathrm{}$ yield, respectively, 45±5 and 200±25 T. The slope ($\frac{d{B}_{c2\mathrm{}}}{\mathrm{dT}}$) near $T_c$ for the Y-Ba-Cu-O compound is about twice as large as in La-Sr-Cu-O. For both compounds the magnetoresistivity indicates a large anisotropy of the critical field. The Sommerfeld parameter $\gamma$ is estimated to be, respectively, 7 and 16 mJ ${\mathrm{}\left(\mathrm{mole}\mathrm{Cu}\right)\mathrm{}}^{-1\mathrm{}}$ ${\mathrm{K}}^{-2\mathrm{}}$, which indicates that the higher $T_c$ of Y-Ba-Cu-O, when compared with La-Sr-Cu-O, might be due primarily to an increased density of states at the Fermi level.