GOLA OR THE SPHERE 75
Brahmagupta (XI, 29-30) criticizes this stanza as follows :
vitriblialagne dfkk^epamandalam tadapamandalaj-utau jya | madhya dykk^epajya naxj^abhatoktanaya tulya \\ drkk§epajyato 'sat taimasad avanater nasalj I avanatinasad grasasyonadhikata ra\igraha;ie. |i
34. The square root of the difference of the squares of the sines of the ecliptic zenith-distance and ofjthe zenith-distance is the sine of the echptic-altitude. *^2-'>* ^1 ^7 A kuvasat k§itije sva drk chaya bhuvj'asardham nabhomadhyat.
The sine of the altitude of the nonagesimal point of the ecliptic is called the drggatijyd.
Drk is equivalent to drgjyd the sine of the zenith- distance of any planet.^
This stanza is criticized by Brahmagupta (XI,
drkk§epajya bahur drgjya l/arno 'nayoh krti%-isesat | miilam drgnatijiva samsthanam ayuktam etad api. 1|
The construction of the second part of the stanza and the exact meaning of drk and chdyd are not clear to me. It seems to mean that when the sine of the zenith-distance is equal to the radius the greatest parallax (horizontal parallax) is equal to the radius of the Earth. Kuvasat ("because of the Earth") seems to indicate that parallax is due to the fact that we are situated on its surface and not at its center, and that parallax, therefore, is the difference between the positions of an object as seen from the center and from the surface of the Earth.
1 Cf. Suryasiddhanta, V, 6; Lalla, Suryagrahapa, 6; Paficasi- ddhardika, IX, 21 and p. 60; Bhaskara, Ga^iMdhyaya, Suryagrahaxia, II, 5-6 (and Vasanabha$ya); BCMS, XIX (1928), 36-37.
