178 Journal of the Asiatic Society of Bengal. [N.S., XV, 
The horizontal parallax of the sun or moon is assumed to 
be equal to the motion of the planet during four nadikas, or 
one-fifteenth part of a day. We thus have 
7 = (daily motion of sun)/15 = 6,/15 for the horizontal 
parallax of the sun, 
n’ = (daily motion of moon) /15 = 6,, /15 for the horizontal 
parallax of the moon, 
where @ is the angular motion of the planet during the day.* 
Since 6 = s/r nearly, where r is the radius of the orbit and s is 
the are traversed in one day, and since, in the Indian system 
earth’s radius; and = becomes equal to s/15r = p/rt which 
is approximately true when r is great compared with p. 
Sometimes the difference between the parallax of the sun 
and moon is given. Thus the parallax in latitude is given in 
forms that may be expressed by 
, 
™3, —7™, = (9, — 6,) (sin z,)/15 = 49’ (sin z,)/7r 
= (sin z,)/70 
where sin z, is the drikshepa (see $ 6(g9)). 
The rule for parallax in longitude may be expressed by 
™, = 7 COS Z, Sin (Ay — A) 
where X is the longitude of the star and Ay is the longitude of 
the nonagesimal.§ 
The Hindu rules for parallax may then be summarised 
thus : 
(i) Horizontal parallax += 6/15 
(ii) Parallax in latitude ™, =7 sin z, 
(ili) Parallax in longitude +, = = cos z, sin Ay — A 
while the corresponding approximately correct formulae are 
(i) sn + = p/r 
(ii) *, = = sin B, sin (y — 8)/sin y 
(iii) =, = = cos B, sin (4, — 4) /cos B 
* The mean values of the daily motion usually given are: moon 
13° 10’ 34”; sun 59’ 8”, which make 7’ = 52:7 and 7 = 3°9; but the texts 
give no actual parallax values explicitly. The Sirya Siddhanta implies 
m’ = 53°3’ and 7’— x = 49’. 
+ The Stirya Siddhanta value is 11,858°7 yoja 
Z Sin 7 = p Ft. 
§ In the texts the meridian ecliptic point is sometimes substituted 
for the n i point. 
