It is gratifying to learn from Mr. Nicholls (May 1955, p. 364) that he is favourably impressed with the exponential function, and it is to be hoped that he, and others interested in stress-strain relationships, may find it to be of practical value.

While the modifications which he suggests are quite legitimate, they tend to mask the essential simplicity of the function. It would be difficult to obtain the asymptotic stress from his first equation. The second can be easily solved for strain, but the converse process is complicated by the fact that the current stress appears both inside and outside the exponential. It is surely much more straightforward, and infinitely quicker, to plot the stress-strain curve from the proof stress data and analyse it in the normal way.