=1938.= Zeno was concerned with three problems.... These are the problem of the infinitesimal, the infinite, and continuity.... From him to our own day, the finest intellects of each generation in turn attacked these problems, but achieved broadly speaking nothing.... Weierstrass, Dedekind, and Cantor, ... have completely solved them. Their solutions ... are so clear as to leave no longer the slightest doubt of difficulty. This achievement is probably the greatest of which the age can boast.... The problem of the infinitesimal was solved by Weierstrass, the solution of the other two was begun by Dedekind and definitely accomplished by Cantor.--RUSSELL, BERTRAND. _International Monthly, Vol. 4 (1901), p. 89._ =1939.= It was not till Leibnitz and Newton, by the discovery of the differential calculus, had dispelled the ancient darkness which enveloped the conception of the infinite, and had clearly established the conception of the continuous and continuous change, that a full and productive application of the newly-found mechanical conceptions made any progress.--HELMHOLTZ, H. _Aim and Progress of Physical Science; Popular Lectures [Flight] (New York, 1900), p. 372._ =1940.= The idea of an infinitesimal involves no contradiction.... As a mathematician, I prefer the method of infinitesimals to that of limits, as far easier and less infested with snares.--PIERCE, C. F. _The Law of Mind; Monist, Vol. 2 (1891-1892), pp. 543, 545._