Natyashastra
मध्यलघुनाथ विद्युत्पादे पादे समं विभक्तेन । आदिलघुना धृतिः स्याद्गणेन योज्या हि मात्रेण ॥ ४८॥
That metre in which the middle syllable is short, and in which the syllables are evenly distributed in each pāda like a flash of lightning (vidyut), is called Dhṛti when it begins with a short syllable. It should be employed with a gaṇa arrangement regulated by mātrās (metrical units).
english translation
madhyalaghunAtha vidyutpAde pAde samaM vibhaktena । AdilaghunA dhRtiH syAdgaNena yojyA hi mAtreNa ॥ 48॥
hk transliteration by Sanscript