In the transpiration method, it has seemed to be the best practice to avoid trumpet‐shaped tubes altogether by cutting the capillary off squarely and sealing it to the remainder of the apparatus without constriction or expansion of any kind. Aside from the mechanical difficulty of meeting this requirement, there have been those who have maintained that a capillary with a trumpet‐shaped exit would be simpler to operate because it would make unnecessary the kinetic energy correction. The theory of the kinetic energy correction was worked out for a tube that was a true cylinder or, at any rate, departed from it but slightly, and therefore it seemed unjustifiable to use modified tubes without further investigation.