358 1W. H. II. Turner and Mr. H. F. 



the exposure was continued for 49 seconds, ending when Mr. \Yyles 

 called " fifty-five." 



>It. The developed photograph shows the spectrum of the 

 corona in two regions situated at the ends of a chord whose length is 

 approximately equal to the radius of the moon's image. 



The radial extension is even less than in Captain Hills's photograph 

 taken atPulgaon in 1898. There is an abrupt fall in the intensity of 

 the marked continuous spectrum at about 2' from the limb, and at 3|' 

 from the limb the spectrum is invisible. 



In the preliminary examination of the spectrum none of the ordinary 

 Fraunhofer lines have been detected, a fact which is of remarkable 

 import when considered in connection with the intensity of the 

 polarisation of the light emitted from the corona. (See below, p. 364.) 



In one of the spectra the hydrogen lines are very strong, viz., Hp, 

 H y , Hj, H c , and Hf. In the other they are barely visible, H y appear- 

 ing only very close to the limb, and not extending more than about 

 a quarter of a minute of arc. The helium lines are strong in one and 

 barely perceptible in the other. In one the calcium lines H and K are 

 intensely strong and broadened, though the edges are defined and the 

 lines very much shifted towards the red end of the spectrum ; in the 

 other, the H and K lines are weak and well-defined narrow lines. It is 

 important to note that the shift of the broad calcium lines is in the 

 direction that one would anticipate if pressure were the cause of the 

 broadening and of the shift. Whilst it seems clear that the presence 

 of the hydrogen, helium, and calcium lines in one and not in the other 

 of the two regions of the corona whose spectra have l>een photographed 

 is probably due to a prominence, this explanation is difficult to recon- 

 cile with the signs of pressure above referred to. 



There are several bright coronal lines discernible in both spectra ; 

 and in the neighbourhood of one of the lines, viz., that of wave- 

 length 4231, there seem to be two dark lines, apparently the only 

 absorption lines visible in the spectrum. 



III. Sprctrum of thf Sttn's Limit <it the E\l of T<>f<ilif>i. Immediately 

 after the end of the exposure of the plate for the spectrum of the 

 corona, the image of the corona was readjusted on the slit, under 

 unexpected difficulties however on account of the faintness of the 

 light. Mr. Wyles called " sixty-four " as I reached the platform again 

 to make the exposures, and the exposures were made as follows : 



Plate No. 7 at 65 



i 8 66 



9 67 



10 68 



H 69 



12 70 



and I gave the signal to Mr. Henn for his last exposure at 71. 



