α Orionis the motion is established; in those of γ and ζ, it is more or less probable, but not at all certain; in all the other cases it is too small to be measured.
This minuteness of the motion makes it probable that these stars are very distant from us, an inference which is confirmed by the smallness of their parallaxes. The careful and long-continued measures of Gill show no parallax to Rigel, while Elkin finds one of only 0".02 to α Orionis.
The general conclusion from our examination is this: The agglomeration of the lucid stars into clusters does not, in the cases where it is noticeable to the eye, extend to the fainter stars.
Let us now study the question on the opposite side. The planispheres show regions of great paucity in lucid stars; is there here any paucity of telescopic stars?
The two regions of greatest paucity are near the equator; one extends through the hour of 0 of R. A.; the other from 12h. 20m. to 12h. 40m. The richness of these and of the adjoining regions may be inferred from Boss's zone of the A. G. Catalogue, including a belt from 1° to 5° of declination. The number of stars in each hour from 23h. to 3h. is as follows:
| In 23h.: | 271 stars. | |
| In 0h.: | 293 stars. | |
| In 1h.: | 299 stars. | |
| In 2h.: | 295 stars. |
These numbers show no paucity in the hour 0, and no excess in the hour 2, which is much richer in lucid stars than the hour 0.
In the strip from 12h. 20m. to 12h. 40m. the catalogue contains seventy-eight stars, a richness of 234 to the hour. In the hour preceding there are 211 stars; in that following, 225. There is, therefore, no paucity in the strip in question.
THE STRUCTURE OF THE MILKY WAY.
The most salient problems suggested by the appearance of the Milky Way are to be approached on lines quite similar to those followed in the last chapter. We begin with a description of this wonderful object as it appears to the observer. We recall that it can be seen through some part of its course on any clear night of the year, and in the evening of any season except that of early summer. We begin with the portion which will be visible in the late summer or early autumn. We can then trace its course southward from Cassiopeia in the northwest. It passes a little east of the zenith down to Sagittarius, near the south horizon. This portion of the belt is remarkable for its diversity of structure and the intensity of the brighter regions.
In Cassiopeia it shows nothing remarkable, but above this constella-
