सिद्धान्तदर्पण (महामहोपाध्याय सामन्त चन्द्रशेखर सिंह - नग्न-नेत्र खगोल वेध एवं गणित महाकोश)

, and between 'गम्यन्तरा' and 'भ्यस्तः'?
Yes: "गत गम्यन्तरा भ्यस्तः".
"शेषस्त त्वाशिवभि (२२५) र्हतः । ७१ ।" - yes, space between 'शेषस्त' and 'त्वाशिवभि'.

Line 16:
Let's look at line 16 again:
"जिस चाप (कोण) की ज्या निकालती है । हो उसे (२२५) से भाग देकर"
Wait, look at "निकालती है । हो उसे":
Wait, is that "निकालनी"?
Look at the letter again:
Could it be "निकालनी"?
In Devanagari, 'त' has a leftward loop/bend that goes down without closing.
'न' has a closed loop on the left.
Look at 'नी' in 'ज्यानी' (line 25), 'उदवाप्त' (line 24), 'केन्द्र' (line 3).
Here, the letter in line 16 has a leftward curve that goes straight down to the baseline. That is definitely 'त'!
Wait, what about the next word?
ह with ै = है.
Then a purna virama: ।
Then ह with ो = हो.
Then उसे.
Wait, why does it say "निकालती है । हो उसे"?
Could it be: "जिस चाप (कोण) की ज्या निकलती है