Some time ago I got a copy of the 1928 version of "The Book of Knowledge", an educational 20 volume series geared to children. It is a fascinating snapshot not only of the state of knowledge at the time (many entries begin with the phrase "We do not know exactly how..." and then go on to ponder what are now scientific commonplaces; perhaps the most remarkable aspect of that is people willing to acknowledge ignorance) but also what was expected for children to learn at the time, and what it was felt they would be curious about. There are quite detailed examinations of engineering, economy, art, history, and geography that might befit a college course these days. There are numerous colored plates showing a variety of plants, birds, and fish. There are sections on poetry and literature, ranging from stuff for the very young on up to Shakespeare. There are crafts (build a shelf out of wooden orange crates!), games, and first aid lessons. There is quite a bit about Canada and its' Prime Ministers (I think the series was geared for both the U. S. and the Great White North). Most of the illustrations are limited to printing in black, white, and red, and by "photogravures", that is, a photo printed on a metal plate (and a word my spellcheck refuses to recognize), another indication of the technology of the time. But as one can see by the example above, quite striking effects could be achieved.