Clausius说得简单明了! 他说: “第二基础原理, 在我所给出的形式中, 断定在自然界中的所有转变可以按一定的方向, 就是我已经假定是正的方向, 而不需要补偿地由它们自己进行; 但是对相反的方向, 就是负的方向, 它们就只可能在同时发生的正转变的补偿下进行. (The second fundamental theorem, in the form which I have given to it, asserts that all transformations occurring in nature may take place in a certain direction, which I have assumed as positive, by themselves, that is, without compensation; but that in the opposite, and consequently negative direction, they can only take place in such a manner as to be compensated by simultaneous occurring positive transformations.)” -- R. Clausius, The Mechanical Theory of Heat, London: John van Voorst, 1867. Ninth Memoir. p. 364.