Humboldt State University

Robert A. Paselk Scientific Instrument Museum

Humboldt's Latin American Expedition, 1799–1804

Richard Paselk, Curator

Engineer’s Transit ("Theodolite")

In his own words in his Personal Narrative of Travels…. Humboldt carried "A theodolite by Hurter, the azimuth circle of which was eight inches in diameter." (Alexander von Humboldt. Personal narrative of travels to the equinoctial regions of the New continent, during the years 1799-1804, by A. von Humboldt and A. Bonpland. translated from the French by Helen Maria Williams, 1814, p 35.)

Regarding the theodolite, Deborah J. Warner, Smithsonian NMAH writes:

"Leonard Digges introduced the word "theodolitus" in his Pantometria (London, 1571). This surveying instrument had a circular ring or plate divided into 360 degrees, and a pivoting alidade with sight vanes at either end. Theodolites of this sort, as well as others with a second pair of sight vanes affixed to the graduated circle, were soon in widespread use. In 1791, George Adams Jr. called this instrument a "common theodolet," reserving the term theodolite for the telescopic instruments with horizontal circles and vertical arcs that had been introduced in London in the 1720s. ... In the 18th century form, the telescope is mounted directly on the vertical arc. In the transit theodolite, which originated in London in the 1840s, the telescope is transit mounted, with a vertical circle mounted at one side. Heinrich Wild’s optical theodolite, introduced in Switzerland in the 1920s, had several new features, including an auxiliary telescope that lets the user read either circle without moving away from the station." *

Selected on-line examples of early 18th and 19th-century artificial horizons that may be similar to Humboldt's include:

  1. Smithsonian NMAH
    1. (c. 1824) http://amhistory.si.edu/surveying/object.cfm?recordnumber=997496
    2. (c. 1820) http://amhistory.si.edu/surveying/type.cfm?typeid=19
    3. (c. 1740) http://amhistory.si.edu/surveying/object.cfm?recordnumber=747813
    4. (c. 1826) http://amhistory.si.edu/surveying/object.cfm?recordnumber=747873
 

transit image  icon

Lietz Co., San Francisco

1938; HSU Geology Dept.

Lietz catalog pages scan icon

Used in surveying for determining both vertical (altitude) and horizontal (azimuth) angles. The transit is similar too and serves the same function as Humboldt’s theodolite by Hurter. The instrument on display appears to be an A. Lietz No. 5E Transit Theodolite with verniers reading to 30 sec on the azimuth circle (see catalog description, Extras). The catalog scan is from the A. Lietz Co. General Catalog, 17th ed. (1938). Complete scans of this catalog are available online at http://archive.org/details/ManufacturersOfEngineeringSurveyingMiningAndNauticalInstruments

Regarding the transit, Deborah J. Warner, Smithsonian NMAH writes:

"The transit was the most important surveying instrument in the United States in the 19th century. But William J. Young, who invented the form in 1831, did not see it as something new, but simply a modification of his new railroad compass. In an advertisement in the American Railroad Journal for March 23, 1833, Young described the transit as "an Improved Compass, with a Telescope attached, by which angles can be taken with or without the use of the needle, with perfect accuracy." J. P. Stabler, Superintendent of Construction of the Baltimore and Ohio Railroad, wrote that the new instrument "leaves the engineer scarcely any thing to desire in the formation or convenience of the Compass. It is indeed the most completely adapted to lateral angles of any simple and cheap instrument that I have yet seen, and I cannot but believe it will be preferred to all others now in use for laying of rails and—in fact, when known, I think it will be as highly appreciated for common surveying." By 1837, the new instrument was known as a transit. The American Railroad Journal added to the historical account in 1855, noting that the first transit "was made by Mr. Wm. J. Young, the accomplished Mathematical Instrument Maker, of Philadelphia, for the Baltimore and Ohio Railroad Company, the Engineers of which made the first suggestions modifying the old Theodolite." **

A 'contemporary' description of the theodolite and its use from Frederick Walter Simms, A Treatise on the Principle Mathematical Instruments Employed in Surveying, Leveling, and Astronomy, Troughton & Simms, London (1834) is available as a pdf here.***

Description

The azimuth and altitude circles are 6 and 4 ½ inches in diameter respectively. They are readable by vernier scales to 30 seconds of arc in azimuth (see image) and one minute of arc in altitude (see image). The compass box is 4 ¼ inches across, reading to single degrees, and adjustable to compensate for magnetic declination (see image). The cap coering the bearing on the altitude circle side is missing (see image above and compare to the image of the opposite side)

* http://amhistory.si.edu/surveying/type.cfm?typeid=19 Downloaded 7 August 2013

** http://amhistory.si.edu/surveying/type.cfm?typeid=20

*** The complete text of this work is available online via google books as well as in various reprints from vendors such as Amazon.


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© R. Paselk

Last modified 16 September 2013