method was described in Puehler's Geometry, published in 1561.[1]
Under any circumstances, it was Tycho Brache who introduced the use of transversals on the graduated arcs of astronomical instruments. He did not use transversal lines, such as afterwards became universally used, but rows of dots, which were fully as convenient, and he showed that the error
Transversal Divisions.
introduced by employing these rectilinear transversals for the division of arcs would not exceed 3″, which would be imperceptible.[2] When Wittich had brought the news of this contrivance to Cassel, Bürgi modified it a little by using lines instead of the rows of dots, and adding a scale on the alidade, the section of which with a transversal line showed the number of minutes to be added to the indication of the preceding division line, while on Tycho's instruments each of the dots corresponded to 1′.
But it was not sufficient to find means to read off the measured angle accurately; it was also of great importance to point the instrument to a star with greater precision than hitherto, and here Tycho had nobody to show the way. Up to his time an alidade had been furnished with two pinnules, one at each end, consisting of a brass plate with a small hole in the middle, and if this hole was made too small, a faint
