40 - Girl in the Golden Atom by Ray Cummings

In a fascinating journey that begins with a golden ring examined under a microscope, a chemist uncovers a vibrant sub-atomic world. There, he encounters a stunning young girl who captivates his imagination. With the help of newfound chemicals that grant the ability to shrink or grow, he and three adventurous friends embark on an extraordinary quest into this miniature realm. (Summary by Richard Kilmer)