Light—as a Feather

On lists of optics “firsts,” sometimes Scottish scientist James Gregory was the first to use a diffraction grating, in 1673. Instead of making one himself, or having it constructed by others (as Thomas Young or David Rittenhouse later did) he simply used a bird feather, observing the splitting of white light into different colors when it passed through the nearly-indentical and equally-spaced barbs. But is this an accurate statement? How did he come to experiment with feathers, what was he hoping to find, and how well did he understand the phenomena he observed? How should we properly calassigy Gregory’s experiment?