Laurent Cassegrain
| Laurent Cassegrain | |
|---|---|
| Born | 1629 Chartres |
| Died | 1693 (aged 63–64) Chaudon |
| Citizenship | French |
| Fields | Optics: Telescope |
| Institutions | Collège de Chartres |
| Known for | Cassegrain reflector |
Laurent Cassegrain (ca. 1629 – September 1, 1693) was a Catholic priest who is notable as the probable inventor of the Cassegrain reflector, a folded two-mirror reflecting telescope design.
Laurent Cassegrain was born in the region of Chartres around 1629 and was the son of Mathurin Cassegrain and Jehanne Marquet. It is unknown what his education was but he was a priest and professor by 1654. He may have been interested in acoustics, optics and mechanics. At the time of his death he was working as a teacher giving science classes at the Collège de Chartres, a French lycée, i.e., a high-school like institution. He died at Chaudon (Eure-et-Loir) on September 1, 1693.
The Cassegrain reflector is a reflecting telescope design that solved the problem of viewing an image without obstructing the primary mirror by using a convex secondary mirror on the optical axis to bounce the light back through a hole in the primary mirror thus permitting the light to reach an eyepiece.
It first appeared in the eighth edition of the 17th century French science journal Recueil des mémoires et conférences concernant les arts et les sciences, published by Jean-Baptiste Denys in April 25, 1672. In that edition is found an extract from a letter written by M. de Bercé, writing from Chartres, where he acted as a representative for the Académie des sciences —scholars of Chartres. M. de Bercé reported on a man named Cassegrain who had written a letter on the megaphone with an attached note describing a new type of reflecting telescope, the Cassegrain reflector, where a secondary convex mirror is suspended above a primary concave mirror. This was around the time of the publication of the construction of the first practical reflecting telescope, Isaac Newton's newtonian reflector. On June 13, 1672, Christiaan Huygens wrote about the Cassegrain design and critiqued it harshly, maybe because Huygens felt Newton's design was being "imperiled" by this alternative. Whatever the motives, the storm of controversy that followed had one lasting effect: Cassegrain's name was forgotten.
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