Calculus Made Easy: Being a Very Simplest Introduction to Those Beautiful Methods of Reckoning:Which Are Generally Called By the Terrifying Names of the Differential Calculus and the Integral Calculus.

The complete text to the first chapter: CHAPTER I. TO DELIVER YOU FROM THE PRELIMINARY TERRORS. THE preliminary terror, which chokes off most fifth-form boys from even attempting to learn how to calculate, can be abolished once for all by simply stating what is the meaning -- in common-sense terms--of the two principal symbols that are used in calculating.
These dreadful symbols are: (1) "d" which merely means "a little bit of." Thus "dx" means a little bit of "x"; or "du" means a little bit...