In an experiment with Foucault's apparatus, the various distances used are as follows :
Distance between the rotating and the fixed mirror $=16 \mathrm{~m}$
Distance between the lens and the rotating mirror $=6 \mathrm{~m}$
Distance between the source and the lens $=2 \mathrm{~m}$. When the mirror is rotated at a speed of 356 revolutions per second, the image shifts by $0 \cdot 7 \mathrm{~mm}$. Calculate the speed of light from these data.