74 



the coelostat, were designed and constructed by Professor Cogshall. 

 Six exposures were made in this camera, of duration one-half second, two 

 seconds, forty seconds, one minute, fifteen seconds, and one-half second. 

 The plates used were Seed's 27, gilt edge, heavily backed. 



If there be intra-mercurial planets, and if they, as do all other bodies 

 of the solar system, move in the plane of the equator of the body around 

 which they are revolving, and, if they are from the sun about the distance 



Fig. II. General view of the camp. Intra-Mercurial cameras to the left, the sixty-foot 

 camera in the center and short focus cameras to the right. 



required by Bode's Law, the major axis of their apparent paths as seen 

 from the earth on the day of the eclipse should have subtended an angle 

 of 23° and the minor axis about 3°. We decided to photograph this region 

 in duplicate. For this purpose we used six cameras of 136 inches focal 

 length, four of which had an aperture of 3i inches and were made by 

 Petitdidier, and two of which had an aperture of 3 inches. These were 

 built by the Alvan Clark and Sons Corporation. These lenses were cor- 

 rected for the minimum focus a —4750, which is well within the region 

 for which the Seed 27 plates, which we used, are most sensitive. All 



