xxvin.] NEWCOMB'S OBSERVATIONS. 439 



have mistaken it for the limb of the sun itself. What this 

 observer, Prof. Newcomb, did, was to erect a screen which covered 

 the moon and a space 12' high round it. The result was, that 

 as soon as he took his station at the commencement of totality, 

 he saw a tremendous extension along the sun's equatorial plane 



FIG. 132. Tracing of Newcomb's observation of 1878, the brighter portion of the 

 corona being hidden by a screen. Shows the equatorial extension and concentric 

 atmospheres. 



on both sides the dark moon, the extension being greater than 

 that recorded in the photograph. It does not follow that the 

 photograph gives us the totality of the extension ; it may be 

 that the extended portions may have been so delicately illumin- 

 ated, that they would not impress their image on the photo- 

 graphic plate in the time during which that plate was exposed, 



