Thermocapillary flow in a bridge of molten silicon under measured oxygen partial pressure in the ambient atmosphere was investigated in terms of fluctuations in the brightness of pixels of CCD images. The fluctuations in the brightness of the CCD images at the silicon surface agree with the temperature fluctuations measured in the bridge by using thermocouples in a mono-ellipsoidal mirror furnace. Moreover. a mode with periodic fluctuations in pixel brightness was found when the temperature difference between the upper and lower interfaces of the bridge decreased from 24.5 to 7.5 K. The Marangoni number corresponding to this temperature difference was estimated to be 700-1700.