“How blessings brighten as they take their flight!”

Source: Argonautica, Book IV, Lines 672–673

Source: Walden, or Life in the Woods

Preface xxx
Variant: When philosophy paints its grey on grey, then has a shape of life grown old. By philosophy's grey on grey it cannot be rejuvenated but only understood. The owl of Minerva spreads its wings only with the falling of the dusk.
As translated by T. M. Knox, (1952) <!-- p. 13 -->
Source: Elements of the Philosophy of Right (1820/1821)
Context: Only one word more concerning the desire to teach the world what it ought to be. For such a purpose philosophy at least always comes too late. Philosophy, as the thought of the world, does not appear until reality has completed its formative process, and made itself ready. History thus corroborates the teaching of the conception that only in the maturity of reality does the ideal appear as counterpart to the real, apprehends the real world in its substance, and shapes it into an intellectual kingdom. When philosophy paints its grey in grey, one form of life has become old, and by means of grey it cannot be rejuvenated, but only known. The owl of Minerva takes its flight only when the shades of night are gathering.

The Newcomes, Ch. 16.

Abençoem-se antes um ao outro, é quanto basta, pudessem ser todas as bênçãos como essa.
Source: Baltasar and Blimunda (1982), p. 175

Attributed as a remark on The O'Reilly Factor on 13 October 2002. There was no episode of "The O'Reilly Factor" on this date.
Misattributed

Scholastic interview (1998)

in Die organische Bewegung in ihrem Zusammenhange mit dem Stoffwechsel, [Julius Robert von Mayer, Die Mechanik der Wärme in gesammelten Schriften, Cotta, 1867, 53-54]
Original: Die Natur hat sich die Aufgabe gestellt, das der Erde zuströmende Licht im Fluge zu erhaschen, und die beweglichste aller Kräfte, in starre Form umgewandelt, aufzuspeichern. Zur Erreichung dieses Zweckes hat sie die Erdkruste mit Organismen überzogen, welche lebend das Sonnenlicht in sich aufnehmen und unter Verwendung dieser Kraft eine fortlaufende Summe chemischer Differenzen erzeugen.