106 On a new Method of viewing the Chromosphere. [Jan. 9, 



The chromosphere is afterwards brought to a focus again at the position 

 usually occupied by the slit of the spectroscope ; and in the eyepiece is 

 seen the chromosphere in circles corresponding to the " C " or other lines. 

 The lens D is used to reduce the size of the sun's image, and keep it of 

 the same size as the diaphragm at different times of the year ; and the 

 lenses F are used in order to reduce the size of the annulus of light to 

 about \ inch, so that the pencils of light from either side of the annulus 

 may not be too divergent to pass through the prisms at the same time, 

 and that the image of the whole annulus may be seen at once. There are 

 mechanical difficulties in producing a perfect annulus of the required 

 size, so one \ inch in diameter is used, and can be reduced virtually to 

 any size at pleasure. 



The proposed photographic arrangements are as follows : — 

 A large Steinheil spectroscope is used, its usual slit being replaced by 

 the ring one. 



A solar beam is thrown along the axis of the collimator by a heliostat, 

 and the sun's image is brought to focus on the ring-slit by a 3|-inch 

 object-glass, the solar image being made to fit the slit by a suitable lens. 



By this method the image of the chromosphere received on the photo- 

 graphic plate can be obtained of a convenient size, as a telescope of any 

 dimensions may be used for focusing the parallel beam which passes 

 through the prisms on to the plate. 



The size of the image of the chromosphere obtained by the method 

 adopted will be seen from the accompanying photograph, taken when the 

 ring-slit was nluminated with the vapours of copper and cadmium. 



As this photograph is not reproduced, it may be stated that the ring- 

 images have an internal diameter of nearly f- of an inch. 



December 6, 1872, at 11.30, December 7, 1872, at 11.30. 



Outer circle 100 ' from inner one. Chromosphere at normal height, except where 

 prominences marked. 



