PHOTOGRAPHS OF THE CORONA. 125 



glasses and we had finished closing the shutters of the dark 

 slides. The " eclipse-clock " was stopped immediately totality 

 was over, so that I had no means of noting exactly the time at 

 which this exposure on the partial phase was given. I had a 

 considerable amount of manipulation to go through to take 

 out one dark slide and to fit in and latch the other, to cross 

 to the front of the instrument and place the cap on the object- 

 glass, to return to the camera end and draw the shutter of the 

 dark slide, and to again go to the front and expose at the object- 

 glass. I estimated the time I took to do this was not less than 

 2 minutes, and that the length of the exposure was 1 J seconds. 

 In reality I must have performed these operations very much 

 more rapidly than I believed it possible, for the measurement 

 of the arc of sunlight gives a very much shorter interval than 

 two minutes from the end of totality not much more, in fact, 

 than a quarter that time. The angle subtended by the cusps 



THE INNER CORONA AFTER THE RETURN OF SUNLIGHT. 



(Drawing by Mr. W. H. Wesley from a photograph by Mrs. Maunder. Reproduced from 

 Knowletlge, May 1898, by permission of the Publishers.) 



at the centre of the moon is 102 33', corresponding to a time 

 of 39 seconds after the end of totality. At this time 0-0056 of 

 the sun's disc was exposed to view. 



Before the plate was developed, when it was taken out of the 

 dark slide the little solar crescent was plainly to be seen like a 

 carraway seed on the sensitive plate. The intense sunlight 

 had acted chemically on the film, and on development the arc 

 of sunlight became intensely solarised and reversed. There is, 

 however, no serious spreading of the over-exposed arc, and the 

 edge of the moon with its fringe of corona is not fogged out. 

 The greatest height to which the corona is seen is 5 minutes 

 of arc, and marks the position of the N.E. ray. This is shown in 

 the little reproduction attached, and for which I am indebted 

 to the kindness of Mr. Wesley. On the negative the S.E. 

 extension is also plainly visible. The average height of the 

 corona is about 4 minutes of arc. A. S. B. MAUNDER. 



