354 Prof. H. H. Turner ai.-l Mr. H. F. NVwall. 



The times after totality are diminished to get true seconds. The 

 numbers in the third column are beats of a metronome, which, though 

 adjusted beforehand, changed its rate, perhaps owing to the fall of tem- 

 perature. Just after totality it was found to l>eat sixty-three times to 

 the minute. Further, the word " One " was called on an actual l>eat 

 which came alxwt 0*5 second after the word " Start " (signifying the 

 commencement of totality) had been called. This signal was given by 

 me from a direct observation of the disappearance of the crescent, and 

 Agreed well with the observations of others. The signal for 15 seconds 

 before totality was given to Mr. Xewall by watching the length of the 

 disappearing crescent on the focussing glass of the camera, and was 

 Approximately correct, though by an oversight no one observed the 

 interval ; but after giving this signal, as I found the direct light of the 

 crescent did not hurt the eyes, I watched that in preference to the 

 image on the glass. I saw the complete ring of the moon's disc quite 

 10 seconds l>efore totality, and from that moment the corona seemed 

 to grow out from the limb in a most beautiful manner. 



18. Programme for tlie Polariscopes. The two polariscopes mounted 

 in the double tube had of course exactly the same exposures as above. 



Between exposures of slides 2 and 3 the Xicol prism and Savart 

 plate of Mr. Newall's polariscopic apparatus were rotated by Major K. 

 O. Foster to the reading indicated by Mr. Xewall's eye observations ; 

 and the slit of my apparatus was also moved by Major Foster to the 

 second position, so that the second pair of photographs gave a different 

 part of the corona from the first. 



The smaller polariscope was exposed from 5 to 60 seconds, counting 

 from the beginning of totality. 



19. Pngnunmefor the Portrait Isns. A Sandell triple-coated plate 

 was exposed in this instrument. The exposure was made by Major 

 Foster from 5 to 60 seconds, counting from the taginning of totality. 



20. The Mnii'liiril frjiHttr*. On the six plates in slides, 1, 2, and 3, 

 Sir "W. Abney's " standard squares " were impressed for photometric 

 observations of the corona. The exposures were to a standard candle 

 at 5 feet from the plate, which is approximately twice as bright as the 

 full moon. Assuming the brightest part of the corona to be as bright 

 AS the average surface of the full moon, the exposures to be given to 

 the candle were calculated as follows : 



An image of the moon in the Dallmeyer lens of 4 inches aperture 

 -would be 1 i inches in diameter. The illumination of the object glass 

 is thus concentrated 



(4/l) 2 times = 7 times. 



Hence the brightest part of the corona will affect the plate about 

 seven times as much as direct moonlight, or three and a half times as 

 much as a candle at 5 feet. 



