[1922]. It seems to be expected of every pilgrim up the slopes of the mathematical Parnassus, that he will at some point or other of his journey sit down and invent a definite integral or two towards the increase of the common stock.—Sylvester, J. J.
Notes to the Meditation on Poncelet’s Theorem; Mathematical Papers, Vol. 2, p. 214.
[1923]. The experimental verification of a theory concerning any natural phenomenon generally rests on the result of an integration.—Mellor, J. W.
Higher Mathematics for Students of Chemistry and Physics (New York, 1902), p. 150.
[1924]. Among all the mathematical disciplines the theory of differential equations is the most important.... It furnishes the explanation of all those elementary manifestations of nature which involve time....—Lie, Sophus.
Leipziger Berichte, 47 (1895); Math.-phys. Classe, p. 262.
[1925]. If the mathematical expression of our ideas leads to equations which cannot be integrated, the working hypothesis will either have to be verified some other way, or else relegated to the great repository of unverified speculations.—Mellor, J. W.
Higher Mathematics for Students of Chemistry and Physics (New York, 1902), p. 157.
[1926]. It is well known that the central problem of the whole of modern mathematics is the study of the transcendental functions defined by differential equations.—Klein, F.