图书介绍：Newton's fundamental discovery， the one which he considered necessary to keep secret and published only in the form of an anagram， consists of the following： Data aequatione quotcunque fluentes quantitae involvente fluxiones invenire et vice' versa. In contemporary mathematical language， this means： "It is useful to solve differential equations". At present， the theory of differential equations represents a vast con- glomerate of a great many ideas and methods of different nature， very useful fo