Title: Heat considered as a mode of motion
Subtitle: being a course of twelve lectures delivered at the Royal Institution ofGreat Britain in the season of 1862
First published: 1863
Description: A great book from a time when the subject was a current topic in science, unlike today.  It's written with an underlying attitude that we don't know everything.  20 years later Planck discovered the quantization of energy.  Excellent explanations and experiments to aid the thought processes behind the molecular theory of matter.  Recommended by Clerk Maxwell, just watch out for talk of the 'ether' and the idea that Francis Bacon's experiments crushing water-filled metal spheres concluding that water came through pores in the metal therefore there are spaces between the metal atoms that water can pass through: he didn't say that, he was proving the slight compressibility of water.  This is WELL worth reading.  There are other books by guys such as Andrew Millikan - BRILLIANT!!
Subjects: Heat, Thermodynamics