An extremely valuable book for public and school libraries, for classroom reference and supplementary reading in history, economics and geography, and for the boy and girl interested in the history of machinery. Miss Hartman has taken each field, gone back to the primitive beginnings and shown how and when machinery was introduced and the changes it made. Spinning, weaving, mining, power, transportation, oil, steel, rubber, communications, building automobiles, wireless, aviation, etc. And the men who brought the changes into being. The last two chapters deal with the resultant problems of labor, and the interdependence of the world, today.