ब्राह्मस्फुटसिद्धान्त (ब्रह्मगुप्त - शून्य, कुट्टक, बीजगणित एवं सम्पूर्ण २१ अध्याय सान्वय सटीक)

HOW TO OBSERVE PLACES OF STARS 343
The author of the Sūrya-Siddhānta then proceeds to notice
the relation of the great circles before mentioned to the horizon,
and observes that whatever place be assumed for the apex of
the sphere, the middle of the heaven for that place is its horizon.
He concludes by showing, that the instrument may be made to
revolve with regularity, by means of a current of water; and
hints, that the appearance of spontaneous motion may be given,
by a concealed mechanism, for which quicksilver is to be
employed. There is a hint of secrecy also in one of the lines,
and it has, therefore, been stated that the construction and the
mechanism of working should be learnt under the guidance of a
teacher.
How to Observe Places of Stars
Details are not available in this connection. The Sūrya-
Siddhānta only hints "that the astronomer should frame a sphere
and examine the apparent longitude and latitude (sphuṭavikṣepa
and sphuṭadhruvaka)". The commentators, however, describe
the manner of making the observation. They direct a spherical
instrument (Golayantra) to be constructed as described above.
This instrument is very much similar to the armillary sphere.
An additional circle graduated for degrees and minutes, is direct-
ed to be suspended on the pins of the axis as pivots. It is named as
Vedhavalaya or intersecting circle, and appears to be a circle of
declination. After noticing this addition to the instrument,
the instructions proceed to the rectifying of the Golayantra or
armillary sphere which is said to be placed, so that the axis shall
point to the pole: and the horizon be true by a water level.
The instrument being thus placed, the observer is instructed
to look at the star Revatī through a sight fitted to an orifice at
the centre of the sphere; and having found the star, to adjust by
it the end of the sign Pisces on the ecliptic. The observer is
then to look through the sight, at the yoga star of Aśvinī, or at
तदाधारयुतेः भार्धमयने विषुवद्वये ।
अयनाद्वयने चैव कक्ष्या तिर्यक्संस्थाऽपरा ॥
क्रान्तिसंज्ञा तया सूर्यः सदा सदापर्य्येति भासयन् ।
चन्द्राद्याश्च स्वरकैः पातैरपमण्डलमाश्रितैः ॥
ततोऽपकृष्टादृश्यन्ते विक्षेपाग्रे स्वपक्रमात् । SuSi. XIII. 3-12