304 



NATURE 



[May 5, 192 1 



we heard that the inn at Durness had been burnt 

 down several years previously, so we proceeded 

 by motor-car along the beautiful side of Loch 

 Shin, and arrived at a place called Rhiconich, at 

 the southernmost end of Loch Inchard. Finding 

 that the hills around were not sufficiently high 

 to obstruct the view of the annular eclipse, we 

 decided to stay at the excellent hotel there for the 

 event. 



We took with us two instruments — one a whole- 

 plate camera fitted with a telephoto lens, and the 



KiG. I. — Our instruments in the ground adjoining the Rhiconich Hotel. 



partial phase. 



other a small Thorpe grating slit spectroscope \ 

 fitted up for taking photographs of the spectra of 

 the limbs where they grazed each other. The 

 spectroscopic part consisted of a box to act as a 

 collimator tube, fitted with a i-in. slit at one end, 

 and a Dallmeyer rapid rectilinear lens at the other. 

 The camera part was also a box arranged to take 

 plate-holders 5 in. by 4 in. at one end, and a 

 Dallmeyer rapid rectilinear 

 lens fitted with a Thorpe 

 grating in front of it. The 

 latter box was placed 

 obliquely with regard to the 

 collimator box, and so ad- 

 justed that both the first- 

 and second-order spectra fell 

 on the photographic plate. 

 This spectroscopic arrange- 

 ment was fitted on a long, 

 stiff plank, made in two sec- 

 tions for the sake of portability, and at the other 

 end were fitted two guides to which was screwed 

 the small framework for carrying a 3f -in. objective. 

 Arrangements were made for propping up this 

 plank in the direction of the sun so that the solar 

 image fell on the slit of the collimator. A. screw 

 adjustment was adapted for raising the plank as 

 the sun increased its altitude. The whole of this 

 NO. 2688, VOL. 107] 



outfit can be seen in Fig. i, as it was in posi- 

 tion on the ground outside the Rhiconich Hotel 

 during the first phases of the eclipse. The whole- 

 plate camera can also be seen a little further 

 away. 



I had to work the instrument completely by 

 myself ; but if I had had some skilled assistance 

 I should have obtained more spectra of the 

 chromosphere. The difficulty was to get the right 

 portions of the crescent exactly on the slit, and 

 then to draw the dark slide and make the ex- 

 posure, the sun mov- 

 ing all the time 

 across the slit. 



The only photo- 

 graph of the chromo- 

 sphere is that shown 

 in Fig. 2. This is an 

 enlargement from the 

 first order of one of 

 the spectra, and 

 shows amongst 

 others the bright 

 hydrogen and cal- 

 cium lines. Each 

 plate exposed gave 

 four spectra— two in 

 each order and two 

 at each limb (upper 

 and lower) of the 

 sun. 



Fig. 3 shows one 



of the numerous 



photographs taken 



vvith the whole-plate 



Young. It was ex- 



the time of mid- 



Photograph taken during the first 



camera by Mr. Allan 

 posed a little before 

 annularity. The eclipse took place under 

 nearly perfect conditions, but there must have 

 been some very high cirrus haze, because 

 during the first partial phases a halo became 

 visible round the sun. This became brighter as 

 the eclipse progressed, and showed the spectrum 



Fig. 2. — The spectrum of 



the chromosphere, showing, amongst other bright lines, the lines of hydrogen 

 and calcium. 



colours distinctly. At two points of this halo, 

 about east and west, mock suns were seen, and 

 these extended right and left and formed prac- 

 tically two spectra lying horizontally, the colours 

 being very distinct. These phenomena were 

 observed by all those who gathered round our 

 camp. 



With regard to the visibility of the planets and 



