The Principle of Similitude

IT is rather curious that Prof, D'Arcy Thompson should refer to Tait's “Properties of Matter,” for I fancy I might claim some part of the credit for the paragraph in question. In a review of the first edition (NATURE, vol. xxxii., p. 314, 1885) I wrote:—“There is one matter suitable to an elementary work which I should be glad to see included in a future edition, viz., the principle of dynamical similarity, or the influence of scale upon dynamical and physical1 phenomena. It often happens that simple reasoning founded upon this principle tells us nearly all that is to be learned from even a successful mathematical investigation, and in the numerous cases where such an investigation is beyond our powers, the principle gives us information of the utmost importance.”