"The Relativity of Time"

Abstract

PROF. H. DINGLE has put forward¹ the view that, while it is correct to deduce the “Fitzgerald contraction” of moving bodies from the Restricted Principle of Relativity, it is incorrect to deduce the slowing down of moving clocks. His main ground is that the second statement is meaningless, because a clock is not a well-defined measuring instrument. If, for example, it takes the form of a stream of equal grains of sand falling regularly in an hour-glass, the time elapsed may be measured equally well by the number of fallen grains, N₁, or by their total mass, N₂, or by their total volume, N₃. Since mass and volume have different transformation laws for moving axes, Prof. Dingle infers that N₁, N₂, and N₃ also have different transformation laws, some showing the retardation and others not.