在气体力学研究中，不可避免地将引用热力学的基本定律，过去在不少工科著者所用的论述中常将传热量Q和气体所做的功W的微增量写为dQ和dW。但从严格的数学理论而言，这是不正确的表达式。笔者在参与《航空空气动力手册》的编审中曾经提出过此问题，在手册的再版时已经改正为δQ和δW。但此后一些气体力学的著作未能引起注意，仍然习惯地写成dQ和dW。为此，在本文中作一个严格的证明，并提出了热力学空间的概念，以澄清以往的混淆。

In the study of pneumatics, it is inevitable to refer to the basic laws of thermodynamics. In the past, a number of engineering authors often wrote heat Q and the micro-increments of the work done by the gas W as dQ and dW, which are, however, not correct expressions as far as a strict mathematical theory is concerned. When participating in the editing of the Aviation Air Force Manual, the author raised this issue. In the second edition of the manual, dQ and dW were corrected to δW and δQ. But some pneumatic works still fail to pay attention to the problem, and are still used to using dQ and dW. In this article, a rigorous proof is conducted and the concept of the thermodynamic space is proposed to clarify the confusion in the past.