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[I feel] engulfed in the infinite immensity of spaces whereof I know nothing, and which know nothing of me. I am terrified. The eternal silence of these infinite spaces alarms me.
Servois' 1813 Perpetual Calendar, with an English Translation
The mathematician Jacques Français (1775-1833) had the following to say regarding Servois' perpetual calendar:
Interestingly, Français extended this compliment two months after Servois publically stated in the pages of the Annales that “I had long thought of calling the ideas of Messrs. Argand and Français on complex numbers by the odious qualifications of useless and erroneous ..." [Servois 1814a, p. 228]. If Français had read Servois’ harsh criticism of his work before he submitted this letter, then we may conclude that Français was definitely a thick-skinned gentleman.
In summary, François-Joseph Servois was a man with a variety of mathematical talents ranging from geometry to calculus, who in 1813 added the workings of the calendar to his mathematical repertoire. Servois' calendar may not be considered ground breaking in the field of mathematics; however, Bradley may have said it best when he wrote that the calendar is “clever, and efficiently manages a large quantity of information in a small space ....” [Bradley, p. 11].
Petrilli, Jr., Salvatore J., "Servois' 1813 Perpetual Calendar, with an English Translation," Loci (June 2012), DOI: 10.4169/loci003884