A feather from the Whippoorwill — Novels

A feather from the Whippoorwill 1
That everlasting-sings!
Whose galleries-are Sunrise-
Whose Opera-the Springs-
Whose Emerald Nest the Ages spin 5
Of mellow-murmuring thread-
Whose Beryl Egg, what Schoolboys hunt
In "Recess"-Overhead!
(F.208/J.161)
[1] feather:: a feather pen. whippoorwill:: one who writes to whip poor will, to stir readers with poor will.
[2] sings:: praises via verses, one's novels.
[3, 4] Sunrise, Springs:: content of these novels.
[5] Emerald:: a printing type of size 6.5 points, alluding publication. the Ages spin:: many years of writing.
[6] thread:: story line, plot.
[7] Egg:: applied contemptuously to a young person (OED 2b). Beryl Egg:: a youth of admiration like some fanciful gem (in the plot). hunt:: to pursue the dream of being an admired youth. Schoolboys:: the author's potential readers.
[8] "Recess":: a period of cessation, or a secret place, in head without the pressure of school classes. Overhead:: up in the air; unrealistic dream for the schoolboys.

Of book types there are twelve regular bodies, viz. Great Primer, English, Pica, Small Pica, Long Primer, Bourgeois, Brevier, Minion, Nonpareil, Ruby, Pearl, and Diamond. Besides these, Minion-Nonpareil is a good deal used; and some founders have introduced intermediate founts, as Emerald. ─ Treatise on Printing and Type-founding (1841)

Dickinson called this poem Pine Bough, an arm being suffered from writing for many years.