I have yet to find much else connecting them, however, apart from Pyle’s childhood fondness for “Darley’s outline drawings to Washington Irving’s stories” and some other scraps.
But here’s something: take a look at Pyle’s “Bringing the powder to Bunker Hill” engraved by John Tinkey for “The Gunpowder for Bunker Hill” by Ballard Smith (Harper's New Monthly Magazine, July 1886).
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“Bringing the powder to Bunker Hill” by Howard Pyle (1886)
And now compare it to “Margaret annoyed by her Brother” engraved by Konrad Huber from Compositions in Outline by Felix O. C. Darley from Judd’s Margaret (New York: Redfield, 1856).
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“Margaret annoyed by her Brother” by F. O. C. Darley (1856)
Call it an act of homage or appropriation or plagiarism, but, subtle differences aside, it’s clear that Pyle based his illustration on Darley’s. After all, it was much easier than rustling up a pair of oxen to draw from - though their proportions might have improved had Pyle observed them in person.