134 A]S!TSrUAL REPORT SMITHSONIAN INSTITUTION, 1942 



This interpretation of the Milky Way was pointed out 190 years ago 

 by Thomas Wright, a pioneer "bird's-eye viewer" of Durham, 

 England. He saw that the hypothesis of a flattened stellar system 

 with the earth near the central plane would satisfactorily explain 

 the Milky Way band as a phenomenon of projection in such a 

 system.^ Our hypothetical observer in Andromeda would see this 

 flattened wheel-shaped system not from the direction of its rim, nor 

 from the direction of its axis, but from an intermediate position, 

 galactic latitude —21°. It would appear in projection, therefore, as 

 an elongated object, perhaps with the axes of the rough ellipse in 

 the ratio of about three to one. There would be a conspicuous 

 globular nucleus of naked-eye brightness. 



We are almost certain now that our galaxy is a great openwork 

 spiral system of stars, perhaps not much unlike the system Messier 83, 

 shown in plate 1. But in linear measure it may be much larger than 

 Messier 83. It has taken a long time to get conclusive evidence on the 

 structure of our own system. We are badly located. There are ob- 

 vious difficulties with residing inside. The meadow violet, no matter 

 how bold and sensitive, is at a disadvantage in meadow topography 

 compared with the bird hovering above. 



For more than a hundred years astronomers have stiiiggled with 

 the problems of the structure of the galaxy. There have been many 

 speculators, but also some hard and systematic observers. Sir William 

 Herschel dominated this field throughout the early part of the nine- 

 teenth century. His surveys of star clusters and nebulae, his measures 

 of brightness and positions of various celestial objects, his interpreta- 

 tions of the accumulating material were so important that he is 

 appropriately considered the founder of sidereal astronomy. Before 

 him the emphasis was on comets and planets and the positions and 

 motions of nearby stars and the laws governing these motions. It was 

 essentially solar-system astronomy that attracted the telescopes and 

 the wisdom of scientists until this German-Anglican organist of Bath 

 devised some instruments; then astronomy turned outward to inter- 

 stellar spaces. 



Sir William Herschel was considerably baffled by the problem of 

 the structure of the galaxy and by the relation of clusters and nebulae 

 to the Milky Way. His successors made many notable contributions, 

 photometric and spectroscopic, to knowledge of the nature of stars 

 and nebulae, but still the large cosmic problems remained baffling. 

 Increasing telescopic strength, however, and the accumulation of many 

 kinds and types of observations, eventaully led to less puzzlement about 



2 For an account of the early cosmic interpretations by Thomas Wright and Imraanuel 

 Kant, see the highly interesting report by F. A. Paneth, The Observatory, pp. Tlfif., June 

 1941 ; also. H. Shapley, Immanuel Kant, 1724-1924, chap. 5, Yale Univ. Press, 1925, E. C. 

 Wllm, ed. 



