Gregorian Type Reflection Telescope

Unsigned, France, late 18th century (around 1780), Brass and gilded bronze, body of the tube sheathed in green shagreen, polished steel mirror. Magnificent travel telescope whose operating principle consists of using a parabolic mirror hollowed out in the center as an objective; a concave mirror with an ellipsoidal surface reflects the beam; the eyepiece is placed behind the objective. This type of telescope, invented by James Gregory in 1663 and produced for the first time in 1668 by Newton, had the advantage of giving, despite its small size, a magnification identical to the immense telescopes of the time. The image is focused by a rod along the tube in working order. The instrument is on a tripod foot with a baluster, the particularity of this model is the hole in the foot which can thus be dismantled and fixed in nature on a tree or a support for outdoor observation. Instrument in very good condition, original optics, the beautifully crafted shagreen piece has been renewed. The lens cap is missing.
Reference: Peter Louwman, A certain instrument for seeing far, p. 127.