then began to take an objective-prism survey of the sky and to classify the resulting spectra.

A first result of this work was the Draper Catalogue of Stellar Spectra, published in 1890. This catalogue contained spectroscopic classifications for 10,351 stars, mostly north of declination -25°. Most of the classification was done by Williamina Fleming. The classification scheme used was to subdivide the previously used Secchi classes