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The hydrostatic pressure dependence of the charge-density-wave onset temperature To in 28-NbSe2 was measured up to 20 kbar. dT~/dP was found to be -{3. 3~0.2) g 10 Kbar '. An examination of existing high-pressure data concerning structural instabilities and superconductivity in both layered and isotropic compounds is made.2H-NbSe, is a trigonal prismatic coordinated layer compound. Qn cooling, it undergoes a structural transition' at the onset temperature T, = 32 K of a incommensurate charge-density-wave (CDW) state' and becomes supereonducting below -7. 2 K. ' 'The superconducting transition temperature To of 2H-NbSe, increases rapidly and nonlinearly with pressure up to -35 kbar, but slowly and linearly beyond -35 kbar. ' This pressure-enhanced superconductivity has been ascribed to the possible suppression of the structural transition by pressure' or to the band broadening due to pressure-promoted interlayer coupling' {it seems possible that the two are related). Our direct pressure mea.surements on T, show that T, decreases with pressure. However, recent results on 2H-TaSe, show that pressure increases T»' and also T,. '

The melting curve of normal hydrogen has been determined up to 52 kilobars between 20 and 300 Kelvins. The results are in excellent agreement with the modified Simon equation proposed for hydrogen below 19 kilobars, but not with the existing theoretical predictions. The results also provide an independent check on the validity of the ruby high-pressure scale at low temperature.

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