J F Fernel wrote three texts which indicate his first studies, mathematics and astronomy. Here-in they are evaluated, but only “Monalospharium” and “Cosmotheoriae” are completely investigated, whilst “de Proportionibus” is simply explained. Thus the measurements involved, the length of a degree of latitude and basic geometry, which includes Euclidian methods are all discussed. It is obvious that J F Fernel is using the work of Claudius Ptolemy, he notes the Almagest text, but his greatest usage is of “Geographike Hyphegesis” when he discusses latitude and longitude, although somewhat at variance.
However all three texts as published are full of errors; the figures are awry and the calculations leave a lot to be desired with a lack of explanation of their basic components.
It is obvious from the construction of the three books that they were compiled between c1520 and 1525 thus allowing publication in 1526 and 1528. The errors are twofold being both original and printer/publisher as the errata do not cover the most obvious. Thus it is clear that the three books were written from notes taken over the 5 years, transcribed at a later date and thus errors were made. However the idea and work involved in measuring the land surface to determine the degree of latitude cannot be criticised; it is a pity as will be shown that a modicum of inaccuracy crept into the methodology and J F Fernel was swayed by spurious measurement comparisons. Some never actually existed and are mathematical enigmas. Basically all three texts require to be carefully read before accepted as correct.
The text is 17 A4 pages and contains 15 A4 diagrams.