Total Solar Eclipse of 1901, May 17-18. 233 



surface 3| x 21 inches, was fixed on a turn-table in front of a tele- 

 scope of aperture 3| inches, and focal length 29 inches. A positive 

 eye- piece with two cross- wires was used, which gave a magnifying 

 power of 19 '2, and whose circular field of view was rather more than 

 1 in diameter. 



The instrument was mounted so that the telescope was parallel to 

 the earth's axis and pointed to the south pole. The grating was used 

 in a manner analogous to that in which the mirror of a polar heliostat 

 is used. The light of the corona was incident at an angle of about 

 57, and the diffracted beam utilised in the telescope left the grating at 

 an angle of about 13. In this position of the grating, the green of 

 the second order was used and the magnifying power of the grating- 

 was approximately one-half, so that the distorted coronal ring was an 

 ellipse, of which the major axis was about twice as long as the minor 

 axis, the minor axis being parallel to the length of the spectrum and 

 perpendicular to the direction of daily motion. No clockwork was 

 used, but a wedge pushed under a wooden arm fixed to the instru- 

 ment and projecting radially outwards from ithe telescope served to 

 give a satisfactory slow motion by slightly turning the whole instru- 

 ment about what may be described as polar pivots. 



The instrument was focussed on the E group of lines about two 

 minutes before totality began. The crescent was small enough to 

 show the lines sharply, though the instrument was so set that the 

 point of second contact was near the end of the major axis of the 1 

 distorted image. 



When I came to make observations of the green coronal ring, I first 

 looked very carefully for fine radial structure ; and finding none, 1 

 altered the focus very slightly. This did not improve matters, so 1 

 reverted to the original focussing, and am quite satisfied about the 

 observation, which could not be more definite. 



The observations were begun after the completion of the third 

 minute of totality and were completed in about 80 seconds. Two 

 ellipses had been drawn beforehand to serve as outline for the distorted 

 limb of the moon ; and on one of these the record of contour lines of 

 the brightness was quickly but carefully sketched. 



Results. The coronal ring was distinctly seen, but there was a good 

 deal of other green light throughout the whole of the field of view, 

 doubtless from clouds. No fine radial structure could be seen any- 

 where round the ring ; but there were two broad patches of the light 

 of " coronium " projecting from the elliptical ring. 



The accompanying figure (fig. 2) shows by the dotted lines the 

 ellipse drawn beforehand, and the contour lines as sketched in during 

 the eclipse. The unbroken lines indicate the results got by projecting 

 the ellipse into a circle and making the corresponding change in the 

 contour lines. 



