In fact an observer would be as likely to make an error
of a minute with the sighting apparatus in Tycho's instrument, as he
would be to make an error of a second with the modern telescope, or,
to express the matter somewhat differently, we may say, speaking
quite generally, that the telescopic method of determining the places
of the stars does not lead to errors more than one-sixtieth part as
great as which are unavoidable when we make use of Tycho's method.
But though this is so apparent to the modern astronomer, it was not
at all apparent in the days of Halley, and accordingly he was sent
off to discuss the question with the Continental astronomers.
Hevelius, as the representative of the older method, which Tycho had
employed with such success, maintained that an instrument could be
pointed more accurately at a star by the use of sights than by the
use of a telescope, and vigorously disputed the claims put forward by
those who believed that the latter method was the more suitable. On
May 14th, 1679, Halley started for Dantzig, and the energetic
character of the man may be judged from the fact that on the very
night of his arrival he commenced to make the necessary
observations. In those days astronomical telescopes had only
obtained a fractional part of the perfection possessed by the
instruments in our modern observatories, and therefore it may not be
surprising that the results of the trial were not immediately
conclusive.
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