Webster’s Revised Unabridged Dictionary · 1913
Observable
Ob·serv′a·ble (ŏb·zẽrv′ȧ·b'l), a. [L. observabilis: cf.F. observable.] Worthy or capable of being observed; discernible; noticeable; remarkable. Sir. T. Browne.
The difference is sufficiently observable. Southey.
— Ob·serv′a·ble·ness, n. — Ob·serv′a·bly, adv.