Page:William Petty - Economic Writings (1899) vol 1.djvu/55

Rh in the history of English medicine before Sydenham could probably say. But one need not be a medical antiquarian to see that, in the most elaborate of these discussions, the one concerning rickets and liver growth, and indeed, throughout all the discussions of this sort, the method of the writer of the "Observations" is distinctly statistical, is marked, indeed, by considerable statistical acuteness, and is scarcely at all diagnostic or pathological, as a physician's method, nowadays at any rate, would probably be. He enquires whether the same disease has been returned in different years under different rubrics; and he finds his answer by investigating the fluctuations from year to year in the number of deaths from each. Moreover, it is in the midst of these discussions of diseases that the variations in the number of those who died of rickets from year to year provokes this curious passage:

Now, such back-startings seem to be universal in all things; for we do not only see in the progressive motion of wheels of Watches, and in the rowing of Boats, that there is a little starting or jerking backwards between every step forwards, but also (if I am not much deceived) there appeared the like in the motion of the Moon, which in the long Telescopes at Gresham College one may sensibly discern. [Page 358 post.]

De Morgan points out the improbability that "that excellent machinist, Sir William Petty, who passed his day among the astronomers," should attribute to the motion of the moon in her orbit all the tremors which she gets from a shaky telescope.

Other peculiarities of the "Observations" which are held by Dr Bevan to indicate Petty's authorship are the "references to Ireland derived apparently from personal observation," and the fact that "Hampshire, Petty's native county, is the only English county mentioned." The latter inference might have been made much stronger for Petty. The author of the "Observations" bases many of his most interesting conclusions upon a comparison between the tables of London mortality and the "Table of a Country Parish," and this country table is unquestionably derived from the parish register of the Abbey of St Mary and St Ethelfleda, at Romsey, the