Page:Popular Science Monthly Volume 58.djvu/424

416 and 25° to 29° of declination, an area of 10°.5. This existence of seven lucid stars within so small an area suggests that they belong together, and may have smaller stars belonging to the group, and making the star-density of this area greater than that of the sky in general.

The question whether there is any corresponding excess of richness in the fainter stars will be decided by a count of those contained in Graham's section of the A. G. Catalogue, which extends to the ninth magnitude. With the area above defined this catalogue gives seventy-one stars. Subtracting the seven lucid stars, we have sixty-four small stars left within the area. To the same belt of declination 336 stars are listed in the twelfth hour of R. A., giving an average of sixty-seven stars to an area equal to that of the cluster. The small stars are, therefore, no thicker within the area of the cluster than around it. It may be added that the seven lucid stars do not seem to have any common proper motion, so that their proximity is probably an accident.

Præsepe.—This object, situate in the constellation Cancer, appears to the naked eye as a patch of nebulous light. It is actually a condensed group of stars, of which the brightest are of the seventh magnitude. The stars of the ninth magnitude included within the area of the group probably belong, for the most part, to it, but they are too few to serve as the base for any positive conclusion.

Orion.—I find by measurement and count that a circle 20° in diameter, comprising the brightest stars of this constellation, contains eighty stars to magnitude 6.3. Of these six are of the first or second, leaving seventy-four from the third to the sixth. The resulting richness is 24 to 100 square degrees, about the average richness along the borders of the galaxy. It follows that this remarkable collection of bright stars has no unusual collection of faint stars associated with it.

A very natural inquiry is whether the bright stars in Orion have any common proper motion, indicating that they form a system by themselves. The answer is shown in the following statement of the proper motions in a century:

For the most part these motions are too small to be placed beyond doubt, even by all the observations hitherto made. In the case of