Thermodynamics is the scientific study of heat. It developed originally on a purely empirical basis, arising in large measure from the efforts of 18th-century and 19th-century engineers to improve the performance of steam-engines. However, although thermodynamics is central to 2Oth-century civilization, it is a subject that novitiates often seem to find both difficult and rather dull; whereas their teachers usually regard it as intriguing and aesthetically satisfying. This stnking difference of perception probably relates to the greater ability of the teacher, or the more experienced student, to encompass as a coherent whole what is actually a very large and all-embracing field of study.