:!.-,ii Prof. II. II. Turner an.l Mi. II. K. NVwall. 



The plate holder wa< of course that of the double tube, us above 

 explained. 



The slit (B) was arranged, as in 1898. in two portions, l.ut was on 

 this occasion made in brass. 



The slit and rhomb were connected by a bar, and could le rotated 

 sympathetically. They were set at such a position angle that the 

 lines of the image parallel to the slit corresponded to vertical lines on 

 the corona ; but this setting was found after the eclipse to be not quite 

 accurate. The setting was not changed during totality, but the slit 

 was moved in the direction of its length, so as to give a different part 

 of the field between the second and third exposures. 



The small polariscope exposed separately resembles the objective 

 prism spectroscope as opposed to the slit spectroscope. The reason for 

 adopting the slit spectroscope form for the instrument alx>ve described 

 is that the angular separation of images given by the large rhomb 

 was not large, and if this rhomb had been simply placed in front of 

 an objective, one image of the corona would have seriously overlapped 

 the other. But a small rhomb (kindly lent me by Mr. Newall) gave a 

 separation of 3, so that when the corona was viewed through this 

 rhomb and an objective the two images polarised in perpendicular 

 planes were clearly separated, though each was projected on the sky of 

 the other. To cut out the sky backgrounds, a slit, of 1 inch aperture, 

 was placed 15 '7 inches in front of the rhomb. 



A<ljnxtiiifiit.<. 



14. Adjust ni<- nt i if (.'<i'h*tnt. The adjustment of the polar axis was 

 made as described in the Report on the Japan Expedition,* by means of 

 the attached declination theodolite. This was a new one, by Messrs. 

 Troughton and Simms, of rather smaller size than the others, with a 

 3-inch circle reading to 1' only. When the three eclipse coelostats 

 were constructed, theodolites were only supplied with two of them ; 

 and as in 1896 and 1898 there were two coelostats at the same station, 

 one theodolite sufficed for adjusting the two. But this arrangement 

 was only provisional, and on the present occasion, when all three 

 ccelostats went to different stations, it became necessary to provide 

 the third theodolite. From previous experience I judged that the 

 smaller size would be sufficient for the purpose. 



The following observations will sufficiently indicate the state of 

 adjustment, those with the level being made on the meridian and 

 compared with the known latitude, so as to give the same sign to the 

 errors as the sun observations : 



* ' Monthly Notices, R.A.S.,' vol. 57, p. 102. 



