This is a lot of 3 Railways of the World in Color by O.S. Nock.  It includes:

The Dawn of World Railways 1800-1850

Railways in the Formative Years 1851-1895

Railways at the Zenith of Steam 1920-40

The books are all from the early 1970s and published by The MacMillan Company.  The format is hardcover that measures 7.75 by 5.5 inches.  They are all in good used condition.  There is some minimal wear on the dust jackets.