^{page 70 note *} A method (whose cheif merit would seem that its results are as likely to be too large as too small) which, is, within the writer's knowledge, used in at least one office.

^{page 72 note *} In point of fact, the division by Dy is done in groups, but that does not affect the argument.

^{page 75 note *} A curve of the second degree can easily be fitted to these four values, practically without error. Working on this assumption, the second difference of ø(x, y) is found to be — 0·000032, a very small quantity, as compared with the values of ø(x, y).