42 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 

 Measurements at ii'' 45"* 



VOL. 52 



Measurements on the Corona 



In the field of the finder telescope were cross-threads, two of which 

 intersected in the center, making an angle of 75°- One of these 

 threads was adjusted along the line of diurnal drift of the sun, as 

 found by stopping the clock of the equatorial. When the moon's 

 image was adjusted tangent to the threads, there were four positions 

 available, according as the moon occupied one of the obtuse angles 

 or one of the acute angles between the intersecting threads. During 

 the eclipse, measurements were made of the corona-brightness at the 

 two positions of tangency in the obtuse angles, and one measurement 

 was made in one of the acute angles. Besides these three positions, 

 two others were employed, situated 1.5' of arc beyond the extremi- 

 ties of the moon's east and west diameter, and one position in the 

 center of the dark moon, making six in all. In view of the symmet- 

 rical character of the results to be given, and of the uncertainty of 

 precise setting on so small an image with the bolometer, it seems 

 unnecessary to specify the first three positions more definitely than 

 to add, that in the two positions of obtuse angle tangency the bolom- 

 eter was central on points 4' of the arc beyond the extremities of a 

 lunar diameter inclined 52.5° to the east and west diameter, and in 

 the position of acute angle tangency the distance from the moon's 

 limb was about 12' of arc. 



Let the six positions be designated in the order described ab^vc as 

 Positions I, II, III, IV, V, and VT. 



