26강:광학적 성질 - 자유/속박전자//양자현상:흡수

Round-17 hunt: picked; source: new-source search (r17: learned societies, museum/library lecture series, summer schools, scholarly conferences, newly covered languages); channel screens (sellers/exam/re-upload/devotional/vendor/events), provenance check, vendor/seller/devotional recheck and quality tier B passed; strict per-title check + final strict pass; oEmbed verified.