The final vowel of viśva is lengthened before mitra when it is the name of a ṛṣi,
As विश्वामित्रः 'the sage Visvamitra'. But विश्वमित्रः 'a boy called Visvamitra'.,
मित्रे चर्षौ
Adhyāya 6 · Pāda 3 · Rule 130
Adhyāya 6 · Pāda 3 · Rule 130
The final vowel of viśva is lengthened before mitra when it is the name of a ṛṣi,
As विश्वामित्रः 'the sage Visvamitra'. But विश्वमित्रः 'a boy called Visvamitra'.,