  From data obtained from the PCA in the 2-11 keV and 11-30.5 keV energy range,
GRS 1915+105 is seen during RXTE observations between 1996 May and October on
two separate branches in a hardness intensity diagram. On the hard branch, GRS
1915+105 exhibits narrow quasi-periodic oscillations ranging from 0.5 to 6 Hz
with ${\Delta \nu \over \nu} \sim 0.2$. The QPOs are observed over intensities
ranging from about 6,000 to 20,000 counts s$^{-1}$ in the 2 - 12.5 keV energy
band, indicating a strong dependence on source intensity. Strong harmonics are
seen, especially, at lower frequencies. As the QPO frequency increases, the
harmonic feature weakens and disappears. On the soft branch, narrow QPOs are
absent and the low frequency component of the power density spectrum is
approximated by a power-law, with index $\sim -1.25$ for low count rates and
$\sim -1.5$ for high count rates ($\gta 18000$ cts/s). Occasionally, a broad
peaked feature in the 1-6 Hz frequency range is also observed on this branch.
The source was probably in the very high state similar to those of other black
hole candidates. Thermal-viscous instabilities in accretion disk models do not
predict the correlation of the narrow QPO frequency and luminosity unless the
fraction of luminosity from the disk decreases with the total luminosity.
