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."
The transit was ideally suited for use in the United States. It was
efficient: since the telescope can be reversed end for end, surveyors could take sights forward and backward along the line. It was rugged: an early commentator noted that a transit "cannot be made totally useless by any accident short of absolute breakage of the parts." This ruggedness was especially important for surveyors who were often many weeks away from any shop that could repair their instruments. And it was economical: throughout the 19th century, a good transit cost no more than $150 and would last a lifetime and beyond. By contrast, an English theodolite may have been more accurate, but it was also less efficient, more delicate, and more costly. The early transits measured horizontal angles only. Later examples were provided with levels and vertical arcs or circles.
Ref: "Invention and Introduction of the Engineer’s Transit," The Engineering News (Oct. 15, 1875): 129–130, and (Nov. 15, 1875): 154–155. The same text, probably written by Alfred Young, appears in many editions of Young & Sons, Price List of Engineering, Mining and Surveying Instruments.