Astronomical survey instrument c. 1860 Brunner a Paris Brass, steel, glass Used to read vertical astronomical angles 30” high and the telescope is 27” long This is a large and impressive instrument. It is a centerpiece of our collection! The instrument’s primary purpose was the reading of vertical angles, for establishing precision time, longitude, latitude and elevation by measurement of the relative locations of stars, and the transits of planets and moons. It is 30” high, weighs approximately 150 lbs. and is built to more of an industrial standard than the typical surveying instrument. Steel bolts are used to fasten all the load-bearing brackets. The large U-shaped frame that supports everything above the horizontal circle is a combination of cast and machined steel. The three-legged leveling base is also machined steel. Many of the motions are controlled by hand screws. Most of these screws are steel except for the hand-turned knurled disk portions which are brass.
 The 13” horizontal circle is silvered, graduated to five minutes of arc and read by two verniers and magnifiers with sunshades to seconds of arc. There is a clamp and spring return tangent motion on the horizontal circle. There are two brass stops on the outer edge that can be positioned anywhere around the circle to control the distance the circle can be rotated. There is a 2” hole that extends from the bottom of the leveling base through the horizontal circle and the large U-frame. We believe it was used to secure the instrument to a pillar or a very large tripod. There are also three brass locking brackets around the top of the hole. The two horizontal magnifiers are attached to a rotatable brass bracket with arms extending outward from the center of the U-frame. There are two 13” vertical circles. Both circles are silvered and engraved to five minutes of arc. Both vertical circles have a clamp and return-spring tangent motion at the bottom. Both clamp and tangent assemblies can be lowered below the circles for easy removal and installation of the circles and telescope assembly.

 To read the vertical circles this instrument includes a total of three spotting microscopes and four filar micrometer microscopes! There are two loose spotting scopes which can be mounted on each circle when the 14-pound counterweight and the precision filar micrometer assembly are not attached. The spotting scopes have the standard crosshair arrangement and allow fast readings in the one-minute range. They both have thumb screw-controlled fine tangent motions. When the spotting scopes are removed, the counterweight and precision filar micrometer assembly can be mounted. It consists of four filar micrometers and one additional spotting scope. The four precision filar micrometer microscopes are normally mounted 90º apart. They are held in place on a 10”, eight spoked brass wheel by large brass clamp brackets with steel bolts. When loosened, the brackets will slide in a grooved slot at the back of the wheel. It is therefore possible to reposition the microscopes in any desired manner. Each filar microscope has a thumbscrew adjusting prism to shine light onto the reticule and circle graduations. The four filar micrometer microscopes have a gauge in the reticule that divides the circle to about one minute and assists with reading the closely spaced parallel crosshairs. The crosshairs are moved by a dial indicator with 60 silvered graduated divisions per revolution and numbered every 10th graduation. It takes approximately 2-1/2 revolutions, or 150 graduations to move the crosshairs five minutes of arc so each dial graduation is equal to two seconds of arc. Theoretically, an experienced user could take accurate readings in the one second range especially when averaging all four micrometers. Both vertical circles are identical and allow the precision filar micrometer microscope assembly to be mounted on either circle. The assembly can be moved from one circle to the other in less than one minute allowing up to eight measurements although we cannot think of an application where this would be necessary. 

The precision micrometer microscope assembly has a vertical arm attached to the bottom which sits between two set screws that hold the assembly in position. The wheel can be rotated slightly by adjustment of the set screws. The microscope assembly and counterweight are held in place by large knurled hand-turned round fasteners. There is a 4-3/4” level bubble with an etched vial-mounted on the bottom of the precision microscope assembly. 

The main telescope has a 5” spotting scope mounted on top which is focused by a slip fit draw tube with standard crosshairs and producing inverted magnified images. The 27’ main telescope rests in two saddles at either end of the mounting shaft. The saddles are open on top as the telescope is very finely balanced and rests solidly in them at all angles with no hold-down clamps. The telescope can be reversed and either end will swing through the U-brackets. Both ends of the mounting shaft have a light path to the reticule. The telescope gives high magnification inverted images. When looking through the filar micrometer eyepiece, there is a measuring gauge across the bottom, three horizontal crosshairs and four stationary vertical crosshairs, plus a fifth vertical crosshair movable by the dial indicator. The silvered, engraved dial is 1-1/2” in diameter and has 100 graduations per rotation with every 10 graduations marked “0-10-20-30-40”, etc. 

The gap between each vertical cross hair is two points on the gauge. The moving crosshair moves one point on the gauge for each full dial rotation. The entire eyepiece moves back and forth about 1/4” by means of a thumbscrew. 

 The eyepiece has a removable right-angle view prism attached to it. There are four small adjusting screws around the eyepiece that require a special tool in the instrument case to be turned, possibly for crosshair and gauge adjustments.

 There is an 11-1/2” striding level that rests on the main shaft. The vial has etched and darkened graduations from 0-40 each way from the center. A brass bracket at one end keeps it steady. The instrument includes the three original wooden cases. The base assembly case 20” x 21” x 27”. The vertical circles, telescope and striding level case which is 14” x 15” x 28". The precision microscope assembly case which is 8-1/2” x 15-1/2” x 17”. We acquired this instrument from a collection in Germany. Before that, it was in the possession of a professor and was family-owned for several decades. At some point in its history, it was used by an astronomical society.

 The telescope and vertical circles retain about 50% of the original lacquer. The microscope assembly retains about 90%. 

The instrument is in excellent working condition throughout and while it has seen substantial use, it was done by trained professionals who took great care of the mechanicals. 

The instrument is signed “Brunner à Paris” on the horizontal circle. Circa 1860. ******** The maker of this instrument is believed to be Swiss-born Johann Josef Brunner aka Jean Brunner (1804-1862), the son of a locksmith. When he was 22, he went to Vienna and learned the art of instrument making. He worked with the famous microscope maker, Vincent Chevalier, and soon distinguished himself for being one of the most active and skillful of the workers. During his spare time, he made his circular dividing engine which was successfully used for years. He moved to Paris in 1828 where he became a famous instrument maker and was known as "Jean Brunner”. In the 30’s, he opened his own workshop in Paris located at 34 rue des Bernardins. There he produced a variety of different types of scientific instruments and microscopes. He exhibited in the French National Exhibition of 1839 and was awarded a silver medal for his apparatus. At the next National Exhibition which was in 1844, he displayed theodolites, microscopes and magnetic compasses but the jury was mostly impressed with his 60 cm astronomical circle. It found the divisions of the circles to be excellent and awarded him the gold medal. In 1845, he moved his workshop to 183 rue de Vaugirard. Brunner was also successful with his spherometers, declination compasses, levels, a clockwork-driven equatorial telescope, etc. He not only developed the new instruments, but he also made some of the precision machine tools and apparatus such as a planing and filing machine, a comparator and a dividing engine, to use in his workshop. When he died, his two sons, Emile (1834 - 1895) and Leon Brunner (1840 - 1894), took over the business as “Brunner Freres” [Brunner Brothers]. They continued inventing and making instruments of the highest quality for 30 years until their deaths in 1894 and 1895 at which time the firm stopped its operations. Reference - Article by Paolo Brenni: Bulletin of the Scientific Instrument Society, No. 49 (1996) “19th Century French Scientific Instrument Makers; XI: The Brunners and Paul Gautier”, pages 3 to 5. http://docplayer.net/34831876-19th-century-french-scientific-instrument-makers.html