o say this is not to disparage the scientific importance of the discovery that mass varies with velocity and of the result of the Michelson-Morley experiment on the velocity of light. Such discoveries were doubtless necessary in order to force recognition of the operational or relational character of scien- tific conceptions. And yet, logically, the way in which space, time and motion, with their various functions, appear in mathe- matical equations and are translated into equivalent formula- tions with respect to one another something which is impos- sible for qualities as such indicates that arelational treat- ment had always been involved. But the imagination of men had become used to ideas framed on the pattern of large masses and relatively slow velocities. It required observation of changes of high velocity, as of light over great distances, and of minute changes occurring at infinitesimal distances to emancipate imagination from its acquired habitudes.