:V72 .Mr. .1. Kv.-r.sliel. 



Nautical Almanac Office is too large, and the limits of error given 

 wriv very misleading. Instead of a duration of 30 seconds, the 

 < < -lipse at my station was never quite total. 



(:>) Iii.xfriniH-iil.t, ,1/,/Wx i if Muiinfiii'i, mi'/ General Arrangement of ('" 



It was my intention originally to take out a fine 18-inch silver-on- 

 glass concave mirror made l>y the brothers Henri, which was given to 

 me by the late Mr. Kanyard. This mirror, having a focal length of 

 117 inches, would have given images on a scale of 1*08 inch to the 

 sun's diameter 



Many experiments were made with this mirror to determine the 

 amount of aberration produced on star images at considerable distances 

 from the axis, and with various apertures. It was found that when 

 the ratio of aperture to focal length did not exceed 1/15, good images 

 were obtained 4 from the normal axis, the aberration being very 

 slight. 



As this would admit of a very wide range of spectrum being photo- 

 graphed with good definition throughout, I decided to adapt my large 

 reflecting telescope for eclipse work. Owing, however, to the difficulty 

 of obtaining a prism of large angle and not less than 6 inches aperture, 

 I had, most unfortunately, to abandon this scheme and construct a 

 much smaller apparatus. 



Through the kindness of Dr. Rambaut I eventually obtained a fine 

 4-inch prism of light flint glass and 45 degrees angle. This prism, which 

 was generously placed at my disposal by Sir Howard Grubb, proved 

 most efficient for the work, although I was unable to utilise the full 

 aperture. 



Three spectrographs were finally made : a reflecting prismatic camera 

 of 3 inches aperture and 74 inches focus, an ordinary prismatic camera 

 of 2 inches aperture and 47 inches focus, and a quartz prismatic camera 

 of 1 inch aperture and 24 inches focus. These were mounted together 

 inside an observing hut, and were supplied with light from a 12-inch 

 ccelostat. 



The Reflect i it ij P/'/.-niiiitif Camera. 



This was an ordinary reflecting telescope with a mirror of 9 inches 

 aperture and 74 inches focus. It was fitted with a strong wooden 

 tube, adapted for carrying two large prisms near the upper end. The 

 prisms used were the 4-inch 45-degree prism, lent me by Sir Howard 

 Grubb, and a 3-inch 60-degree prism lent me by Dr. Common. These 

 were mounted eccentrically within the tube, in such a manner that the 

 incident light, after passing through the prisms, made an angle of about 

 1 with the normal axis of the mirror. After reflection from the 

 mirror the rays returned over the upper surface of the 60-degree 

 prism, and came to focus about an inch outside the end of the tube. 



