“ In astronomy the “mean sun” is a fictitious sun which moves uniformly in the celestial equator and has its right ascension always equal to the sun’s mean longitude. The time recorded by the mean sun is termed mean-solar or clock time; it is regular as distinct from the non-uniform solar or sun-dial time. The “mean moon” is a fictitious moon which moves around the earth with a uniform velocity and in the same time as the real moon. ”

“ In mathematics, the term “mean,” in its most general sense, is given to some function of two or more quantities which (1) becomes equal to each of the quantities when they themselves are made equal, and (2) is unaffected in value when the quantities suffer any transpositions. ”