THE reply by Mr. N. K. Adam, in NATURE of September 26, p. 464, to my note on the cause of surface tension, contains a very great deal with which I heartily agree. His method of calculating the shape and size of the drop from the surface energy is, of course, perfectly valid; as so often happens in mechanics, there are different ways of resolving the forces, each way bringing out features that the other ways do not. I can even agree with him that thinking in terms of the tension has not been found to be a good “means of gaining insight into the molecular structure of surfaces”, and should not urge the actual use of this conception upon any one who prefers not to use it. Where I cannot quite follow him is in concluding that, because the tension has proved to be conceptual dynamite in practice, therefore the tension itself has no physical existence.