Sentence:  And then it started like a guilty thing / Upon a fearful summons. I have heard, / The cock, that is the trumpet to the morn, / Doth with his lofty and shrill-sounding throat / Awake the god of day; and, at his warning, / Whether in sea or fire, in earth or air / The extravagant and erring spirit hies / To his confine: and of the truth herein / This present object made <WSD>probation</WSD>. 
Meaning of the word marked with <WSD> tags:  The act of testing; proof