Laurent Cassegrain
(
French:
[lo???
kasg???]
;
c.
1629
? 1 September 1693) was a
Catholic priest
who is notable as the probable inventor of the
Cassegrain reflector
, a folded two-mirror
reflecting telescope
design.
Biography
[
edit
]
Laurent Cassegrain was born in the region of
Chartres
around 1629 and was the son of Mathurin Cassegrain and Jehanne Marquet.
[1]
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.
[2]
At the time of his death he was working as a teacher giving science classes at the College de Chartres, a French
lycee
, i.e., a high-school like institution. He died at Chaudon (
Eure-et-Loir
) on 1 September 1693.
[3]
Connection with the Cassegrain reflector
[
edit
]
Light path in a
Cassegrain Reflector
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 memoires et conferences concernant les arts et les sciences
, published by
Jean-Baptiste Denys
on 25 April 1672. In that edition is found an extract from a letter written by M. de Berce, writing from
Chartres
, where he acted as a representative for the Academie des sciences —scholars of Chartres. M. de Berce 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
.
[4]
On 13 June 1672
Christiaan Huygens
wrote about the Cassegrain design and critiqued it harshly, maybe because Huygens felt Newton's design was being "imperilled" by this alternative.
[5]
Whatever the motives, the storm of controversy that followed had one lasting effect: Cassegrain's name was forgotten.
The identity of this "Cassegrain" has had many theories. His only known publication was the letter on the megaphone/reflecting telescope in the 25 April 1672
Recueil des memoires et conferences concernant les arts et les sciences
. For a long time, reference works were forced to report his first name as "not conclusively known". The
Encyclopædia Britannica
(15th edition, 1974), for example, only goes as far as listing "Cassegrain, N." (this, in turn, seems to come from
Ferdinand Hoefer
's
Nouvelle biographie generale
,
Paris
, 1855). Other sources have suggested the "N." stood for Nicolas. Some sources (such as
La grande encyclopedie
, 9, 696) claim his name to be Guillaume, a metal-caster and sculptor who is mentioned in the accounts of king
Louis XIV
's buildings between 1684 and 1686, and also in a Paris notarized act from 1693. Another name put forward is Jacques, a
chirurgeon
(i.e.,
surgeon
) mentioned in the
Memoires de l’Academie des sciences
as having found, in 1691, a piece of magnet in the steeple of Chartres Cathedral, then being repaired after being damaged by inclement weather.
In 1997 two French astronomers, Andre Baranne and Francoise Launay, after a long and meticulous investigation including a search for unpublished manuscripts and the analysis of parish registers in the places where Cassegrain lived (Chartres first and then
Chaudon
, near
Nogent-le-Roi
), identified
Laurent Cassegrain
as the most likely candidate.
[6]
The crater
Cassegrain
on the
Moon
is named after him, even though his true identity was not known at the time of the naming.
See also
[
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]
Notes
[
edit
]
- ^
Hockey, Thomas (2009).
The Biographical Encyclopedia of Astronomers
.
Springer Publishing
.
ISBN
978-0-387-31022-0
. Retrieved
August 22,
2012
.
- ^
Note: Based on whether the letters described by M. de Berce are from Laurent Cassegrain
- ^
Chaudon web page on Laurent Cassegrain
(in French)
- ^
In February 1672,
Isaac Newton
reported his first invention, the
Newtonian telescope
to
Christiaan Huygens
, who promptly published it. Huygens also wrote to
Jean Gallois
to report the invention, and that letter was published in the February 29, 1672 issue of the
French
Journal des scavans
. In
England
, Newton's invention appeared a month later, in the Philosophical Transactions of March 25, 1672 (number 81). The
Journal des Scavans
was completed by the
Recueil des memoires et conferences concernant les arts et les sciences
, published by
Jean-Baptiste Denys
.
- ^
English, Neil (2018).
Chronicling the Golden Age of Astronomy A History of Visual Observing from Harriot to Moore
.
Springer Publishing
.
ISBN
978-3-319-97706-5
. Retrieved
August 24,
2021
.
- ^
Fred Watson (2006).
Stargazer: The Life and Times of the Telescope
. Da Capo Press, Incorporated. p. 131.
ISBN
978-0-306-81483-9
.
External links
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]
References
[
edit
]
- Christiaan Huygens
,
Reflexions sur la description d'une lunette publiee sous le nom de M. Cassegrain
(Letter #1892, addressed to
Jean Gallois
),
Œuvres completes
, vol. 7, pp. 189-191
, 1888.
- Andre Baranne and Francoise Launay,
Cassegrain: a famous unknown of instrumental astronomy
, Journal of Optics, 1997, vol. 28, no. 4, pp. 158?172(15)