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To the pure geometer the radius of curvature is an incidental characteristic - like the grin of the Cheshire cat. To the physicist it is an indispensable characteristic. It would be going too far to say that to the physicist the cat is merely incidental to the grin. Physics is concerned with interrelatedness such as the interrelatedness of cats and grins. In this case the "cat without a grin" and the "grin without a cat" are equally set aside as purely mathematical phantasies.
The Expanding Universe..
Servois' 1813 Perpetual Calendar, with an English Translation
Recommendations for Use in the Classroom
This article provides teachers of mathematics with an original source to use with their students, which, unlike much source material, does not require advanced mathematical understanding. The article could be used as the foundation for many classroom activities in a number of different mathematics courses, as well as student-centered research projects.
For instance, the material in this paper could be used to create an activity in a high school or liberal arts mathematics course. There are many websites which provide easy instructions for creating perpetual calendars, such as Robinson . Teachers can create their own perpetual calendars and have students discover concepts, such as corresponding months and the behavior of leap years. Additionally, teachers can have students create their own perpetual calendars. Teachers could encourage multiculturalism through this project by allowing students to create perpetual calendars for different cultures or religions; for example, one based on the Hebrew calendar.
Additionally, the material in this paper could also be incorporated into a history of mathematics course. If possible, it is always better to learn about the history of mathematics from a mathematician's own words. Servois' “Calendrier perpétuel”  can easily be used for such a purpose. Students in a history of mathematics course could investigate the mathematical advances occurring in France around this time, other mathematical works of Servois, or the history of the calculation of the date of Easter Sunday.
Furthermore, Servois' 1813 paper provides students with an opportunity to conduct research on the history of mathematics. Open questions include, for instance:
Petrilli, Jr., Salvatore J., "Servois' 1813 Perpetual Calendar, with an English Translation," Loci (June 2012), DOI: 10.4169/loci003884