Total Solar 



of 1900 (May 28). 



361 



and adjusted the exposing shutter. I am very much indebted to him 

 for his admirable precision in carrying out the programme of ex- 

 posures. 



The programme was carried out as follows : 



Three plates were exposed. 



Plate X, 1. For the brightest chromospheric lines, at the beginning 

 of totality a short exposure, about 1^ seconds. 



This plate was to be exposed at the signal "Start," given by 

 Professor Turner, and was to be closed between the time- 

 keeper's calls " one " and " two." 



It was actually exposed at the signal " Start," and closed at 

 the time-keeper's call " three." The time-keeper found that the 

 first beat of the metronome after " Start " came so soon that he 

 did not call "one," but called the next beat "two "without 

 calling " one " at all. The exposure was thus probably 

 2 seconds. 



Plate X, 2. For the green coronal ring a long exposure, about 

 40 seconds. 



This plate was to be exposed as soon after Plate X, 1 as the 

 change of plate holders would allow, and was to be closed at 

 the call "fifty-five." 



It was actually exposed at " nine " and closed at " fifty-five," 

 and thus had an exposure of about 46 beats. 



Plate X, 3. For the Fraunhofer lines immediately after the end of 

 totality for comparison with any chromospheric lines that might 

 appear on Plate X, .1. 



This plate was to be exposed when I gave the signal " Now," 

 and was to be closed 1 second later. 



It was actually exposed at " seventy-one," and closed at 

 " seventy-two." 



Results. The Plates X, 1 and X, 2 show faint images, but have not 

 been examined carefully yet ; a cursory examination shows that () 

 only a single chromospheric line appears on X, 1 ; and (6) continuous 

 spectrum appears on X, 2, but no marked coronal ring is discernible. 



Plate X, 3 is a strong spectrum, showing the curved Fraunhofer 

 lines between wave-lengths 5050 and 5460 ; the linear dispersion on 

 the plate is, roughly speaking, 5 tenth-metres per millimetre. 



Remarks. In an eclipse with longer duration of totality, the pro- 

 cedure here described should give good results for the green coronal 

 ring. The plates used were Edwards's Isochromatic Snapshot plates. 

 It should be remembered that the effective aperture of the camera, 

 viz., a little less than F/17, was rather dangerously small. 



