Interesting photograph by Paul and Prosper Henry of the cluster of Hercules. These French astronomers and optics enthusiasts invented numerous instruments, telescope and camera lenses for the Paris Observatory in order to observe and record distant stars. In 1887 they participated in the development of the photographic map of the skies. (Bernadette Pordoy)

It's very fascinating to see the small print [Cliché original.] of the same image in the upper right corner of the enlargement [Cliché Agrandi]. Almost like a collage.

Albumen print from “La Photographie astronomique à l’Observatoire de Paris et la carte du ciel" Gauthier-Villars, Paris, 1887.

Print ca. 13,1 x 8,2 cm
Small print ca. 1,4 x 1,1 cm
Mount ca. 18 x 11,8 cm

A complete edition of this book is kept in the collection of the Rijksmuseum in Amsterdam, see last image for reference only.