In the 1920s, empirical equations were used to find the power of V that appeared in the exponent of a semi-logarithmic equation assumed to describe experimental CFE results. In 1928, theory and experiment were brought together to show that (except, possibly, for very sharp emitters) this power is V. It has recently been suggested that CFE experiments should now be carried out to try to find the power (κ) of V in the pre-exponential of the following empirical CFE equation: