IT is evident that the apparent area of an irregular surface will depend on the size of the object used for measuring it. This has been clearly expressed by Constable (NATURE, Sept. 15, p. 399), the ...

As has already been pointed out (Proc. Roy. Soc., A, vol. 119, p. 196; 1928), the area of an activated contact catalyst will vary with the method of measurement adopted. It is thus essential to the ...