Ch.I. south AMERICA. 9 



half, the difference of longitude, by account, would 

 have been only 57°. This error in marking the log- 

 line is common both to the pilots of Spain and other 

 nations ; and this, like many other faults in naviga- 

 tion, remains uncorred:ed for want of attention. 



The diftance between the knots on the log-line, 

 fhould contain ^^-o of ^ ^-^^il^i fuppofing the glafs to run 

 exadly half a minute : and though all agree in this re- 

 fpe6t, yet not in the true length of the mile, which ought 

 to be determined by the moft exad menfu rations, as 

 thofe of M. Caffini in France, ours in the province 

 of Quito, or thofe of M. Maupertuis in Lapland. 

 If the length of the degree be computed according to 

 M. Caffini's m.eafures, 57060 toifes, a minute or 

 geographical mile will contain 951 toifes, or 5706 

 royal feet, of which nearly equal to 47 feet 6f 



inches ; and as the Paris foot is to that of London as 1 6 

 to 15 *; this, when reduced to Englifh meafure, makes 

 near 50 feet 8 J inches. And this is the true diftance 

 between each knot on the log-line. 



This menfuration, which fhould have been hitherto 

 the rule obferved, is not exad, when compared to that 

 which has been found from invefligating the figure of 

 the earth, v^hich is difcoveredto be very different from 

 what it has been imagined ; fo that it is not furprizing 

 that there fhould be found confiderable differences in 

 nautical calculations. 



* * According to the late regulation of the royal fociety of London, 

 and the meafures fent by it to the academy of fciences at Paris, and 

 with which I was favoured by Martin Folkes, Efq; the worthy pre- 

 fident of that fociety, the Paris foot is to that of London as 864 to 

 3 1 1, which fliews how erroneous thefe are publifhed by father 

 Tofca ^ 



a The Paris foot is divided into jz inches, and each inch into 12, 

 lines ; wherefore, if we fuppole each line to be divided in 310 parts, 

 The Paris foot will be 1440 parts. 

 The London, i^S*^ 

 Thefe proportions were fettled by the royal acad'^my of fciences at 

 Paris, in their treatife of the figure and magnitude of the earth. Part 

 x'u Chap. 5, which Hiews the erroneoufnefs of the above, A. 



The 



