Report on the Solar Eclipse Expedition to Sahdol. 9 



graphed on it at different parts of the field, the source of light being 

 a paraffin lantern. The adjustment to focus was made by moving the 

 secondary magnifier, rings of paper placed between flanges on the 

 adapter carrying the magnifier and its mounting giving the means of 

 doing this with great nicety. By this method, in which the error 

 from imperfect focus is doubled by the double passage of the rays 

 through the telescope, it was found that a displacement of the 

 magnifier through the thickness of a sheet of paper (0*005 inch), 

 representing l/20,000th part of the focal length, made a sensible 

 difference. The focus was thus obtained with great accuracy, as is 

 evidenced by the sharpness of the image on the photographs taken 

 during the partial phase. 



The photographs with exposures of 8 sees., 10 sees., and 20 sees. 

 all show coronal structure up to the edge of the plate, the streamer 

 in the S.W. being particularly bright. A hurried eye estimation 

 made by me during the 20 seconds' exposure gave the extreme 

 extension of this streamer as about two-thirds of the distance of 

 Venus from the Sun's centre, or about 3| from the limb. The field 

 being necessarily limited by the diameter of the concave enlarging 

 lens (3 in.), it would be desirable to have one made of larger diameter 

 for future eclipses so as to allow of the use of larger plates. 



A comparison of the whole series of photographs indicates a close 

 correspondence between the coronal streamers and the prominences 

 visible, this correspondence being particularly striking in the case 

 of three prominences in the N.W. quadrant from which three coronal 

 rays rise, arching over at a distance of about 7' from the limb and 

 uniting to form one component of the striking long double ray in 

 that quadrant. Other prominences on the Sun's limb appear also to 

 be associated with extensions of the corona. The form of the corona 

 bore a closer general resemblance to those of 1886 and 1896 as 

 photographed than would have been expected considering that the 

 date of the eclipse was so much nearer the epoch of minimum sun- 

 spots, and in this connection it may be noted that there were three 

 important groups of spots on the Sun about the time of the eclipse, 

 and that a series of magnetic disturbances of moderate amount were 

 recorded at Greenwich just prior to the eclipse, from January 15 to 21 

 continuously, indicating an unusual state of magnetic activity in 

 close correspondence with the solar activity as evidenced by the 

 Sun spots. 



