Northfield, MN: Goodsell Observatory of Carleton College, 1914. Wraps. First Edition. , -330, ; -390,  pp. Light gray paper wraps with minor browning to edges, fraying and chipping along spine, ink library stamp on cover of each volume. Clean within. Very Good.
The Hertzsprung–Russell diagram (or H-R diagram) is a scatter diagram showing the relationship between the intrinsic luminosity (brightness) of stars and their temperatures (as indicated by their “spectral type” or color). The diagram presents stellar evolution--a star begins its life in one place on the chart and moves across the chart during its lifetime. The H-R relationship was discovered independently by Einer Herzsprung and Henry Norris Russell. This two part paper contains a presentation by Russell on his research and H-R diagram.