The history of this type of instrument begins with the "Improved
Surveying Compass" described in William J. Young’s 1830 patent
application. The patent was granted in 1832, withdrawn for technical reasons,
and granted again in 1834. Young designed this instrument so that surveyors
could measure horizontal angles either with or without reference to magnetic
north. The design proved to be especially useful for railroad surveys, and most
examples were sold for that purpose. An advertisement in the American
Railroad Journal for March 23, 1833, carried several testimonials. One from
a civil engineer stated: "Having for the last two years made constant use
of Mr. Young’s ‘Patent Improved Compass,’ I can safely say I believe it to
be much superior to any other instrument of the kind, now in use, and as such
most cheerfully recommend it to Engineers and Surveyors." The term
"Railroad Compass" came into use after the expiration of Young’s
patent in the mid-1840s.
Young’s patent describes a compass with two plates of nearly equal
diameter. The upper plate carries the sights, ring, and needle, as in an
ordinary compass. It also has an opening through which is visible a small
portion of the finely graduated circle on the lower plate, and a vernier for
subdividing the divisions of that lower circle. The two plates are moved
relative to one another by tangent screw, by rack and pinion, or "by any
other method that may be preferred." By replacing the vertical sights with
a telescope, Young transformed the Improved Compass into the Surveyor’s
Transit.
