In the first place, no want of accuracy whatever is imputable to Shakspeare.
The beaver of a helmet is frequently used by writers, improperly enough, to express the helmet itself. It is in reality the lower part of it, adapted to the purpose of giving the wearer an opportunity of taking breath when oppressed with heat, or, without putting off the helmet, of taking his repast. As it was raised up for this purpose, it could of course be let down again; but it could not be let down on either of the before-mentioned occasions. The visiere or visor was another moveable part in the front of a helmet, and placed above the beaver in order to protect the upper part of the face; and being perforated with many holes, afforded the wearer an opportunity of discerning objects: and thence its name. It was made also to lift up when the party either wanted more air, or was desirous of seeing more distinctly. It was perhaps never down but in actual combat; whilst the beaver would be thrown up or kept down at the wearer's discretion, without much difference, except that in battle it would be closed, and at meals, or for additional coolness, thrown up. In short, the visor or beaver could only be let down after they had been already lifted up; and when a writer speaks of their being down, it is generally meant that the helmet is closed.
To exemplify the above remarks, correct representations of a real helmet and its parts are here given. See likewise Grose's Treatise on ancient armour, plates 10, 26, 30.
Fig. 1. The helmet closed.
Fig. 2. The visor thrown up, the beaver down.
Fig. 3. The visor and beaver thrown up.
Fig. 4. The visor detached.
Fig. 5. The beaver detached.
