Total Eclipse of the Sun as observed at Ovar, Portugal. 401 



the instruments used, are shown in the accompanying diagram, which 

 is enlarged about four times. 



is the centre of the sun's disc ; AB is the bright arc as seen 

 10 sees, before totality, and is 70. The centre of the arc, C, which is 

 about 1 from the equator, is 16 above the point D where the arc is 

 vertical and could be made to touch the slit. . The slit, which is repre- 

 sented by dotted lines, cut the bright arc between C and D, the hori- 

 zontal distance between C and D being ^V-h of an inch. The time for 

 the first exposure, viz., 10 sees, before totality, was given to the 

 observers by the Astronomer Royal from the length of the rapidly 

 diminishing arc as seen by him on the ground glass of the corono- 

 graph. This time appears to have been given correct to about 1 sec. 



The position of the image on the slit was not changed for the 

 spectrum of the corona, which was obtained near the point of second 

 contact. 



For the " flash " at third contact the slow motion of the heliostat 

 was used, making the sun's image travel in the direction OC of the 

 diagram, the amount of the displacement being determined by watch- 

 ing the sun in the attached theodolite. The position of the slit 

 relatively to the bright arc is shown in the second diagram ; in thi& 

 case the slit was not nearly tangential to the sun's limb. 



The photographic plates used were Ilford " Empress " for the first 

 " flash " photograph with the flint spectroscope and for both the 

 " flash " photographs with the quartz. An Ilford " Ordinary " was- 

 used for the second "flash" photograph with the flint. Cadett " Light- 

 ning plates " were used for both photographs of the corona spectrum. 



Spectrum of the Sun's Limb. The series of spectra of the limb show 

 a large number of lines, but they have not yet been examined in detail. 

 With the flint spectroscope, a spectrum is obtained extending from 

 F to K. This is good from F to h. With the quartz the spec- 

 trum reaches from h to A. 3300, and is in good definition to about 

 A 3450. The photographs taken with the quartz spectroscope at the 



VOL. T.XVII. 2 G 



