We present follow-up time-series photometric observations that confirm and extend the results of the significant discovery made by Barlow et al .
( 2008 ) that the Hot DQ white dwarfs SDSS J220029.08 - 074121.5 and SDSS J234843.30 - 094245.3 are luminosity variable .
These are the second and third known members of a new class of pulsating white dwarfs , after the prototype SDSS J142625.71+575218.3 ( Montgomery et al .
2008 ) .
We find that the light curve of SDSS J220029.08 - 074121.5 is dominated by an oscillation at 654.397 \pm 0.056 s , and that the light pulse folded on that period is highly nonlinear due to the presence of the first and second harmonic of the main pulsation .
We also present evidence for the possible detection of two additional pulsation modes with low amplitudes and periods of 577.576 \pm 0.226 s and 254.732 \pm 0.048 s in that star .
Likewise , we find that the light curve of SDSS J234843.30 - 094245.3 is dominated by a pulsation with a period of 1044.168 \pm 0.012 s , but with no sign of harmonic components .
A new oscillation , with a low amplitude and a period of 416.919 \pm 0.004 s , is also probably detected in that second star .
We argue , on the basis of the very different folded pulse shapes , that SDSS J220029.08 - 074121.5 is likely magnetic , while SDSS J234843.30 - 094245.3 is probably not .