He declares, with some degree of exultation, that he has no idea of a cannon charged with double cracks; but surely the great author will not gain much by an alteration which makes him say of a hero, that he redoubles strokes with double cracks, an expression not more loudly to be applauded, or more easily pardoned than that which is rejected in its favour.  That a cannon is charged with thunder, or with double thunders, may be written, not only without nonsense, but with elegance, and nothing else is here meant by cracks, which in the time of this writer was a word of such emphasis and dignity, that in this play he terms the general dissolution of nature the crack of doom.

The old copy reads,

They doubly redoubled strokes.

I.ii.46 (401,8) So should he look, that seems to speak things strange] The meaning of this passage, as it now stands, is, so should he look, that looks as if he told things strange.  But Rosse neither yet told strange things, nor could look as if he told them; Lenox only conjectured from his air that he had strange things to tell, and therefore undoubtedly said,

  What haste looks thro’ his eyes? 
  So should he look, that teems to speak thinks strange.

He looks like one that is big with something of importance; a metaphor so natural that it is every day used in common discourse.

I.ii.55 (402,1) Confronted him with self-comparisons] [Theobald interpreted “him” as Cawdor; Johnson, in 1745, accused Shakespeare of forgetfulness on the basis of Theobald’s error; and Warburton here speaks of “blunder upon blunder.”] The second blunderer was the present editor.

I.iii.6 (403,5) Aroint thee, witch!] In one of the folio editions the reading is Anoint thee, in a sense very consistent with the common accounts of witches, who are related to perform many supernatural acts by the means of unguents, and particularly to fly through the air to the places where they meet at their hellish festivals.  In this sense, anoint thee, Witch, will mean, Away, Witch, to your infernal assembly.  This reading I was inclined to favour, because I had met with the word aroint in no other authour till looking into Hearne’s Collections I found it in a very old drawing, that he has published, in which St. Patrick is represented visiting hell, and putting the devils into great confusion by his presence, of whom one that is driving the damned before him with a prong, has a label issuing out of his mouth with these words, OUT OUT ARONGT, of which the last is evidently the same with aroint, and used in the same sense as in this passage.

I.iii.15 (405,8) And the very points they blew] As the word very is here of no other use than to fill up the verse, it is likely that Shakespeare wrote various, which might be easily mistaken for very, being either negligently read, hastily pronounced, or imperfectly heard.