These numbers constitute an arithmetical progression of the rth order.
The equivalent volumes and topic parameters are tabulated: From these figures it is obvious that the first three compounds form a morphotropic series; the equivalent volumes exhibit a regular progression; the values of x and t,t, corresponding to the a axes, are regularly increased, while the value of w, corresponding to the c axis, remains practically unchanged.
Of course there may be single taxes which are progressive in form, such as the licence tax in France, or the income tax in Great Britain, where progression is established by abatements, or the death duties, where progression by scale is very common.
" Now for the interpolation of the rest, I considered that the denominators I, 3, 5, &c., were in arithmetical progression; and that therefore only the numerical coefficients of the numerators were to be investigated.
It was early perceived by Huxley, Cope and many others that Cuvier's broad belief in a universal progression was erroneous, and there developed the distinction between " persistent primitive types " (Huxley) and " progressive types."