Total Eclipse of the Sun a.s observed at Ovar, Portugal. .''99 



successful, and show the greatest extension, that taken with the 

 " Abney " lens showing rays which can be traced on the east side to a 

 distance of more than 2 from Sun's centre, and on the west side to a 

 distance of fully If . This is further than they could be traced visually 

 under the atmospheric conditions at Ovar, where the observers traced 

 them to a distance estimated at I; of distance of Mercury from centre, 



III. TJte Spectroscopic Cameras. 

 (By F. W. DYSON.) 



Instruments. The spectroscopes used were two kindly lent by 

 Captain Hills, and employed by him in the Indian Eclipse of 1898, 

 January 22. The details of their adjustments as used at Ovar are as 

 follows : 



The width of the slits were adjusted by a method given by Mr. 

 Newall. The third diffraction image of the slit, viewed by putting the 

 eye near the position of the plate, was made to come on the edge of 

 the object-glass by altering the width of the slit, and the slit left at this 

 reading. 



The length of the spectrum on the plate for spectroscope No. 1 was 

 3^ inches from H/s (A 4861) to K (A 3934), and for spectroscope No. 2 

 2 inches from A 4100 to A 3500. 



Both spectroscopes were mounted horizontally, and were supplied 

 with light by a heliostat furnished with a 12-inch flat mirror. 



Erection and ^djuxtincnt of Instruments. As the nature of the ground 

 was unsuitable for brickwork or concrete piers, three of the boxes in 

 which the instruments were carried were filled with stones and the 



