National Geographic : 1939 Feb
TIME AND TIDE ON THE THAMES 241 Photograph by B. Anthony Stewart SEVEN SPRINGS IS CONSIDERED BY MANY THE TRUE SOURCE OF THE THAMES Protected by walls, these cold, clear springs flow the year round, near Cheltenham. Eleven miles south, near Cirencester, is another source, known as Thames Head, which is sometimes dry. From Seven Springs, in the hills, to its mouth, the river measures about 215 miles (page 239). Photograph by Maynard Owen Williams ROWBOATS GO "OVER THE ROLLERS" INSTEAD OF BEING "LOCKED UP" AT TEDDING TON, JUST ABOVE LONDON To save time, work, and water, small craft on reaching such upper-Thames locks are pulled over escalatorlike tracks (page 247). Larger and heavier craft pass through water-filled locks.