ABSTRACT
Astronomical instrument-making may be justly regarded as the most refined of the mechanical arts, and that in which the nearest approach to geometrical precision is required, and has been attained. It may be thought an easy thing, by one unacquainted with the niceties required, to turn a circle in metal, to divide its circumference into 360 equal parts, and these again into smaller subdivisions. But the most important of the class of errors arise from the non-existence of natural indications, other than those afforded by astronomical observations themselves, whether an instrument has or has not the exact position, with respect to the horizon and its cardinal points, the axis of the earth, or to other principal astronomical lines and circles, which it ought to have to fulfil properly its objects. With regard to errors of adjustment and workmanship, not only the possibility, but the certainty, of their existence, in every imaginable form, in all instruments, must be contemplated.
