. . . And on to the rings of Saturn? On the face of it the topic seems made for Asimov, and he certainly achieves a solid workmanlike treatment. But since how-and-why rather than who-did-what-when is where his heart lies, he doesn't breathe a great deal of life into the chronological organization the subject demands. Once past a summary of early astronomy and that first serendipitous 16th century combination of lenses, he settles down with relish to the technical aspects. The early telescopes did not instantly unlock the universe. Calculation of actual distances bad to await improvements in the accurate measurement of time, and the science of optics was still limited by uncertainties about the behavior of light and the imperfect state of the lens-maker's art. As late as the 18th century, Newton himself, unaware of the spectrographic properties of different kinds of glass, maintained that chromatic aberration (the partial prismatic effect of light passing through refracting lenses, resulting in colored rings around the image) could not be corrected. Asimov follows the development of reflecting telescopes (which brought a welcome reduction in the length of the instruments), the parallactic measurement of the nearest stars, and the improvement of both reflecting and refracting telescopes until the earth's atmosphere itself became the greatest technical hindrance to accurate observation. The last great innovations--photography and spectrography--were succeeded by discoveries beyond the visible spectrum which have established the primacy of the radio receiver over the eye. Optical telescopes remain more able to scan wide areas of sky, but at present radio telescopes give much better resolution. An interesting subject worked out with smooth efficiency, if not the ultimate Asimovian energy.