"Calculus Made Easy" by Silvanus P. Thompson (1910). It is availably freely online via the Gutenberg project and many other forms too. Chapter 1 is probably the best mathematics chapter I have ever read [0]. In two paragraphs, it beats most other calculus books.
Came here to tell this. IIRC, a newer edition of the book by Martin Gardner was published in 1998 with some notable updates. I read the newer one when I was in high school and as with all other Martin Gardner books, this was an absolute gem to learn and understand calculus.
[0] http://calculusmadeeasy.org/1.html