Brillouin scattering provides a possibility to determine accurately ac
oustic velocities. However, usual Brillouin scattering measurement can
not be performed on a molten sample. The S/G/S Brillouin scattering me
thod was thus proposed. In the present work, we report acoustic veloci
ty measurements on two glasses (water-white glass and window glass) at
high pressures and temperatures, where a sharp turning point in the v
elocity-temperature plots indicates the passing of the glass transitio
n temperature theta(g). An ultrasonic method was used for measurement
of the velocity of the compressional wave at high temperature and pres
sure up to 1500 degrees C and 6.5 GPa. The high-temperature experiment
s at different pressures have shown the same phenomenon as found in S/
G/S Brillouin scattering measurements.