No heat engines have a thermal efficiency of 100%. That is,no heat engines absorb heat and convert it completely into work. There is nothing in the first law of thermodynamics that denies this possibility. （没有一种热机的效率为100%,也就是说,没有一种热机将吸收的热全部转化为功｡这与热力学第一定律并不相矛盾｡）
The first law requires only that the energy output of an engine, in the form of mechanical work, shall equal the difference between the energies absorbed and rejected in the form of heat. An engine which rejected no heat and which converted all the heat absorbed to mechanical work would therefore be perfectly,consistent with the first law.（第一定律认为:发动机输出机械功的多少应该等于吸收的热量与排放的热量之差｡因此不排放热量并将吸收的热量全部转化为机械功的发动机是完美的,这与第一定律相一致｡）
There is another principle,independent of the first law and not derivable from it, which determines the maximum fraction of the energy absorbed by an engine as heat that can be converted to mechanical work The basis of this principle lies in the difference between the natures of internal energy,and of mechanical energy. The former is the energy of random molecular motion; the latter is the energy of ordered molecular motion. Superposed on their random motion,the molecules of a moving body have an ordered motion in the direction of the velocity of the body. The total molecular kinetic energy associated with the ordered motion is what we call in mechanics the kinetic energy of the moving body. The kinetic energy associated with the random motion constitutes the internal energy. When the moving body makes an inelastic collision and comes to rest,the ordered portion of the molecular kinetic energy becomes converted to random motion.Since we cannot control the motions of individual molecules,it is impossible to reconvert the random motion completely to ordered motion.We can,however,convert apportion of it;this is what is accomplished by a heat engine.（有另一个与第一定律无关的定律,也不能由第一定律推导而得｡该定律确定了热机转换为机械功热量的最大值｡该定律的基础是内能和机械能之差｡前者是分子随机运动的能量;后者是有序分子运动的能量｡伴随着分子的随机运动,一个运动物体的分子沿着物体运动的方向做有序的运动｡这种分子有序运动的全部动能就是我们在机械学里所说的运动物体的动能｡分子随机运动的动能就构成了内能｡当一运动物体作非弹性碰撞并最终停下时,分子有序运动部分的动能转换为分子随机运动部分的能量｡因为我们不能控制单个分子的运动,所以再将分子随机运动部分的动能全部转换为分子有序运动的动能｡但是,我们能转换其中的一部分,这个工作就是由热机来完成的｡）
The impossibility of converting heat completely into mechanical energy forms the basis of one form of the second law of thermodynamics. The second law deals with directly measurable quantities such as heat and work,and can be stated apart from any molecular theory. One statement of the second law is as follows. No process is possible whose sole result is the absorption of heat from a source at a single temperature and the conversion of this heat completely into mechanical work.（不能将热全部转换为机械能的事实构成了热力学第二定律的基础｡第二定律描述的是直接能测量的量入热､功等,它能脱离分子理论来进行描述｡第二定律有如下一种描述方法:这样一种过程是不能实现的:从单一热源吸热,并将热全部转换为机械功｡）
The first law denies the possibility of creating or destroying energy; the second denies the possibility of transforming heat from a source which is at the same or a lower temperature into work.（第一定律否定了创造能量和毁灭能量的可能性,第二定律否定了这样一个现象:将从单一热源或低热源吸收的热量转换为机械功｡）
