HALLEY. 41 



60. The political fame of John de Witt has overpowered 

 that which he might have gained from science, and thus his mathe- 

 matical attainments are rarely noticed. We may therefore add 

 that he is said to have published a work entitled Elementa linea- 

 rum curvarum, Leyden 1650, which is commended by Condorcet ; 

 see Condorcet's Essai...d'Analyse... i>age CLXXXiv. 



CI. We have now to notice a memoir by Halley, entitled An 

 estimate of the Degrees of the Mortality of Mankind, dravm from 

 carious Tables of the Births and Funerals at the City of Breslaiv; 

 with an Attempt to ascertain the Price of Annuities upon Lives. 



This memoir is published in Vol. xvil. of the Philosophical 

 Transactions, 1693 ; it occupies pages 596 — 610. 



This memoir is justly celebrated as having laid the foundations 

 of a correct theory of the value of life annuities. 



62. Halley refers to the bills of mortality which had been 

 published for London and Dublin ; but these bills were not suit- 

 able for drawing accurate deductions. 



First, In that the Number of the People was wanting. Secondly, 

 That the Ages of the People d}dng was not to be had. And Lastly, 

 That both London and Dublin by reason of the great and casual 

 Accession of Strangers who die therein, (as appeared in both, by the 

 great Excess of the Funerals above the Births) rendered them incapable 

 of being Standards for this purpose; which requires, if it were possible, 

 that the People we treat of should not at all be changed, but die where 

 they were born, without any Adventitious Increase from Abroad, or 

 Decay by Migration elsewhere. 



63. Halley then intimates that he had found satisfactory data 

 in the Bills of Mortality for the city of Breslau for the years 

 1687, 88, 89, 90, 91 ; which *'had then been recently communi- 

 cated by Neumann (probably at Halley's request) through Justell, 

 to the Royal Society, in whose archives it is supposed that copies 

 of the original registers are still preserved." Lubbock and Drink- 

 luater, page 45. 



64. The Breslau registers do not appear to have been pub- 

 lished themselves, and Halley gives only a very brief introduction 



