TEE TOTAL SOLAR ECLIPSE. 101 



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 de- 

 grees 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 de- 

 termination 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 Observa- 

 tory 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 con- 

 junction, 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 



