Scoresby's crow's nest, Melvillized

Still looking at Melville's rewrite of Scoresby in chapter 35 of Moby-Dick.  After finding another example there of Melville's use of "owing to" when revising a source, I thought it would be fun to compare more of Scoresby and Melville, setting the original and rewrite side by side.  Here goes then...

Source:  

William Scoresby, An Account of the Arctic Regions vol. 2 (Edingurgh and London, 1820), 304-205.

Melville's rewrite of Scoresby shown below within brackets, in bold blue from

Herman Melville, Moby-Dick (1851), chapter 35.

... A piece of canvas tied round the head of the main-top-mast, and heel of the top-gallant-mast, extending only from the cap to the cross trees, or at best a canvas stretched round the base of the top-gallant rigging, but open on the after part, was the most complete contrivance of a crow's nest, until a few years ago, when my Father invented an apparatus, having the appearance of a rostrum, [enviable little tents or pulpits, called crow's-nests] which afforded an admirable defence against the wind....The form is cylindrical; open above and close below.  [In shape, the Sleet's crow's-nest is something like a large tierce or pipe; it is open above, however, where it is furnished with a movable sidescreen to keep to windward of your head in a hard gale.] ...The entrance is by a trap-hatch at the bottom. It is fixed on the very summit of the main-top-gallant mast, from whence the prospect on every side is unimpeded. [Being fixed on the summit of the mast, you ascend into it through a little trap-hatch in the bottom.] On the after side is a seat, with a place beneath for a flag. In other parts are receptacles for a speaking trumpet, telescope, and occasionally for a rifle piece*, with utensils for loading. [On the after side, or side next the stern of the ship, is a comfortable seat, with a locker underneath for umbrellas, comforters, and coats. In front is a leather rack, in which to keep your speaking trumpet, pipe, telescope, and other nautical conveniences.]  For the more effectual shelter of the observer, when in an erect posture, a moveable screen is applied to the top on the windward side, which increases the height so much as effectually to shield his head. [paraphrased already, above, "where it is furnished with a movable sidescreen to keep to windward of your head in a hard gale."]  When the ship is tacked, nothing more is necessary for retaining the complete shelter, than shifting the screen to the opposite side, which is done in an instant.

*[Scoresby's footnote:] The rifle has been occasionally used for shooting narwhales: when fired at from the deck, it is almost impossible to kill them, partly on account of the resistance of the water, which the ball must pass through, and partly on account of the deception in their position, produced by the refractive property of the water. Shooting from the mast head nearly perpendicularly downwards, in a great measure obviates both these inconveniences.  [rewritten by Melville as follows:  "When Captain Sleet in person stood his mast-head in this crow's-nest of his, he tells us that he always had a rifle with him (also fixed in the rack), together with a powder flask and shot, for the purpose of popping off the stray narwhales, or vagrant sea unicorns infesting those waters; for you cannot successfully shoot at them from the deck owing to the resistance of the water, but to shoot down upon them is a very different thing."]