Besides group shots of a mix of instrument types, this ‘Special Exhibit’ includes a graphometer, invented around 1598, which consists of a semi-circle dial with two independently pivoting alidades, so the instrument can measure vertical angles as well as horizontal depending on how it is held. Graphometers usually incorporate a magnetic compass. Because of its simple, compact and portable design, the graphometer was popular with surveyors for over two centuries, preferred over the theodolite by the majority well into the 1800s; a two-telescope brass transit with a simple azimuth ring made in the late 1700s in Liege, Belgium. The instrument would be placed on a staff and one of the independently pivoting telescopes sighted on a stadia staff or other reference, the other scope rotated to back site in the opposite direction or to turn an angle; a sighting level with an open ended rectangular tube without lenses, rather with thin brass cross bars at the objective lens position, from the early-1800s, the bulls eye bubble and black paint are a later addition; and a Troughton & Simms brass theodolite with the scope riding on the vertical arc, c1840. Some of the instruments in these picture are shown in greater detail in the various sub-categories of surveying instruments that follow.

Even though the theodolite was designed around 1556, it took three hundred years to really catch on with surveyors. It is made with a flat horizontal disk like the astrolabe that is divided into 360 degrees, with or without a compass mounted in the middle, and a circular or half circle plate or ring oriented vertically or at right angles to the horizontal dial and graduated over 90 degrees for measuring vertical angles. This two dimensional measuring capability is called altazimuth, the instrument more commonly called, ‘two-circle’. Theodolites developed into many different models, designs and sizes for specialized applications and diverse environments that can vary from high and airy mountain peaks to deep and cramped underground mines. For example, mine theodolites typically have either pivoting auxiliary telescopes mounted atop the vertical circle or the primary scope to allow sighting vertically up or down a shaft or winze or orient to nadir, or a hollow base axis so the surveyor can sight vertically down. In the early 1900s makers began enclosing the circles on theodolites for protection in the field and mines, and in the late 1920s added interior optics with protruding magnifying scopes to read the dials. Compact theodolites with a half-arc vertical dial that is breached at the top and bottom to create two arcs are called, ‘Mount Everest type’. Micrometer theodolites that allow greater precision became available early in the 1900s. Theodolites with optical distance measuring capabilitiea are called tacheometers. The gradioplane is a specialized theodolite that appeared about 1910. It has a normal horizontal dial and compass but in place of a vertical dial it sports a large helical ‘gradienter screw’ that allows measurement of very small vertical angles. Transit theodolites are designed with telescopes that swing in the vertical plane forward and backward 180 degrees in order to back sight. (More about transit levels below.)

Levels made for tripods differ from theodolites by lacking a vertical circle, half-circle or arc. From development of William Gravatt’s level in 1830 through the twentieth century, simple leveling telescopes with or without compasses have been called ‘dumpy levels’, referring to Gravatt’s design which had a high diameter to length ratio. They are designed both as simple leveling sights, commonly with a compass or azimuth dial, and as transit levels with a scope that can be rotated to back sight. The original transit level, invented in 1734, was called the ‘Y’ level, because the removable telescope rests on ‘y’ or ‘u’ shaped collars with a similar shaped hinged clip that swings and locks over the telescope to hold it in place. Thus the scope can be easily removed and placed to back site in the opposite direction. From the mid-late-1800s, most transits and transit levels manufactured have been designed with telescopes that swing in the vertical plane forward and backward to back-sight, just like a transiting theodolite. The surveyor’s compass, designed in the mid-1850s, is simply a large, 5 to 6 inch diameter compass in a brass case with hinged sighting alidades, spirit level and vernier scale. Some have interchangeable alidades and telescopes. It usually has a threaded base for mounting to a tripod or staff. Mine dials are similar except later models were more compact, fitted with smaller dials, the vertical dial mounted low against the horizontal dial and equipped with a short telescope sometimes mounted to a gimbaled frame that rotates to offer vertical sightings both up and down.

Alidades take various forms but can be as primative as two sights mounted along a pole or string, or at opposite ends of an arc or ring. The sights on a rifle barrel might be considered alidades. Alidades facilitate sighting a straight line, lining up one’s position with a distant object and measuring horizontal and usually vertical angles as well. As a plane table tool, they are attached to scaled parallel rules, placed over a map or chart on a table, typically a table atop a tripod, and used to survey or map a local site. The parallel rule provides the means to draw lines in parallel to the sight direction and to plot features to scale relative to a stationary position. Modern alidades are usually equipped with a telescope and come with or without a vertical arc. Plane alidades with only sighting arms hinged to a ruler were made into twentieth century. Today, the alidade principle of ancient times is incorporated into more sophisticated devises like electronic theodolites and the ‘total station’.

Small hand-held and staff-mount surveying instruments and accessories come in many forms for many purposes. They include such devices as the circumferentor and similar graphometer (described above), surveyor’s sextant, rangefinders, pocket mining transits, hand and reflecting levels, rule clinometers, clinometers/compasses, mountain barometers, measuring chains and tapes, cross-staff heads, spirit levels, artificial horizons, traverse tablets, stadia staffs, surveyor’s slide rules and plumb bobs or plummets. The Abney level, invented in 1870 and called ‘The Miniature Theodolite’, consists of a 4 to 6-inch long rectangular telescope on the side of which is mounted a semicircle arc, graduated in degrees for measuring vertical angles, and a small spirit level. While viewing through the telescope at any angle a mirror reflection of the spirit bubble can be viewed through a small window to line up horizontal or determine an angle of inclination. Rule clinometers are elegantly fashioned multi-purpose instruments. They consist of a thick, hinged, boxwood foot rule in which an inclinometer with vernier scale is mounted at the hinge position. They incorporate a spirit level, retractable alidade sights and brass cased compasses, the latter either stationary or gimbaled. The Crellin's Complete Traverse Table is a simple mechanical traverse marker that operates logarithmically. It consists of a brass tablet with a row of brass levers that can be rotated for counting through 1 to 10, 10 to 100, and 100 to 1000, mush like an abacus. Plumb bobs are quite varied and some large brass or nickel-brass plumb bobs quite elegant. Some come with a detachable end that screws off to give access to a spool with string that feeds out a hole to tie to a tripod, plane table or other devise for leveling.