Observation of waves in the Si I line formed in the photosphere (top) and the He I line formed in a chromosphere (bottom). The images show a time series of Doppler velocities along the line of sight measured in the two spectral lines along a spectrograph slit placed across the umbra of a sunspot (NOAA9176) observed by the VTT on October 1, 2000 at latitude 10°S and heliocentric longitude 19°W. The measured velocities have been Fourier-filtered to show only the waves in the range of 3-min period.