Fig. 1. The spiral pattern of the Galaxy according to B. Y. Mills ; it is defined by the observed steps in the distribution of radio brightness with longitude (see Figure 2). Directions of well-defined steps are indicated by the lines of sight radiating from the sun; less pronounced ones are shown as dashed lines. Note that the lines of sight are tangent to the corresponding spiral arms; that at 351° is incorrectly drawn too near the center and is actually tangent also.