¹ Professor Skempton points out in a letter to the Editor that his work on the mills in Derbyshire and Shrewsbury was carried out jointly by himself and Mr H. R. Johnson of Sheffield University (Trans. Newcomen Soc. 1956, in the press). He also points out that it is incorrect to describe (as some have done) the Shrewsbury Mill as the first completely iron-framed building; it had, like all these mills, heavy brick load-bearing external walls and only the interior structure was of iron.