This short book on the subject of thermodynamics is based on a series of lectures I gave for the possible benefit of some 500 sophomore engineering students at Rensselaer Polytechnic Institute during the spring term of 1968. These lectures were not in any sense meant to replace a textbook, nor were they intended to cover the same ground in the same way as a textbook. I intended them to supplement the textbook, and it was my primary hope that they might help the student over the very difficult ground characteristic of the early stages of an initial course in thermodynamics.
I offer this material in print for the same reason. It falls in the classification of a visual aid, though of a very oldfashioned but perhaps still not outmoded type. It is intended not for experts, but for students. I have left rigor for the textbook and from the very beginning have directed my efforts here toward showing the plausibility and usefulness of the basic concepts of the subject.