Page:Popular Science Monthly Volume 65.djvu/105

equator on May 18—exactly in it on June 3—which was a favorable circumstance. Again, there is little probability that such bodies would be as much as nineteen degrees from the sun, and a width of six degrees would therefore allow for a considerable departure of the orbit planes from the solar equator.

Professor Perrine has deduced the following interesting results from these observations:

Before drawing any conclusions from these observations it is desirable to determine the relative brightness and size which any bodies in this region would have, by means of other members of the solar system. The asteroids seem to be best suited for this investigation, as they probably most nearly resemble the hypothetical intramercurial planet in size and condition of surface. The determination of the diameters of the four principal asteroids by Barnard [as below] renders these bodies the most suitable for such work.

Asteroid.		Visual Magnitude.	Distance, Miles.
	Ceres	7.5	485
	Pallas	8.5	304
	Juno	9.5	118
	Vesta	6.6	243
		——	——
	Arithmetical mean	8.0	290

The above magnitudes are those obtained at the Harvard College Observatory by photometric means. The results show such a wide range in albedo that the simple mean has been taken to represent the relations between magnitude and diameter for the group.

Assuming that the distance of the 'mean asteroid' from the earth is 153 million miles, we find that such a body, if transported to a distance of twenty-eight million miles from the' sun (corresponding to an elongation distance of eighteen degrees), and seen from the earth at elongation, would be one hundred and ten times as bright. This corresponds to an increase in brightness of 5.1 magnitudes. Such a body would be relatively brighter near superior conjunction, and fainter near inferior conjunction. An intramercurial planet at the above mean distance from the sun would have to be only one tenth the diameter of the mean asteroid to appear of the same brightness.

From the dimensions and brightness of the four brighter asteroids we find that on the average one of these bodies, three hundred miles in diameter, seen at the opposition distance of the mean asteroid, would appear as of the eighth magnitude. Hence an intramercurial planet of similar constitution and thirty miles in diameter should appear as a star of eighth magnitude. If the hypothetical planet were closer to the sun, the difference of brightness and size would of course be correspondingly greater than that found above.

These observations indicate, therefore, with the exception to be noticed later, that there is no planetary body as bright as 5.0 visual magnitudes within eighteen degrees of the sun whose orbit is not inclined more than seven and one fourth degrees to the plane of the sun's equator. They further indicate that in two thirds of this region there was no such body as bright as seven and three fourths magnitude. The possible exception to be noted is that at the time of the eclipse such a body or bodies might be directly in line with the sun or with the brightest portion of the corona. The area covered by the moon's disk and corona was, however, less than one two-hundredth that of the region