THE CORONA VISER 257 



within a degree or two of 7° per hour. Thus by taking a series of 

 photographs over a period of several hours it was possible to determine 

 definitely whether or not the image in question was associated with 

 the sun or with the apparatus. In addition to this test, for the prom- 

 inences, there was the spectrohelioscope at hand by which a direct 

 comparison could be made. Another test applied to the prominence 

 images was furnished by their color. A red glass filter, such as the 

 Schott RG 2 which has a cut-off just below the Ha line, reduced the 

 general glare level by about 30 times whereas its reduction of the light 

 of the prominences which is a maximum at this wave-length was not 

 nearly so great. 



Results 



The prominences shown in Fig. 5 are among the first of which good 

 images were obtained. Seven photographs were taken of them be- 



Fig. 5 — •Prominences taken with red filter on Feb. 21, 1938. 



tween 16^ 58°^ and 19^^ 11°^ G.C.T. on February 21, 1938, some in 

 white light and the others with the red filter in front of the photo-cell. 

 This particular photograph was taken in red light; those taken in white 

 light were of considerably less contrast. 



Figure 6 is another one of the many prominence photographs that 

 have been taken with the apparatus. These are the prominences that 

 were present around the sun at 18^ 30™ G.C.T. on October 31, 1938. 

 This was also taken with the red filter. 



Figure 7 shows a pair of bright prominences photographed in white 

 light on October 3, 1938. 



Figure 8 shows a jet or flare in the corona that was photographed 

 on October 18, 1938. It is one of 11 photographs that were taken 



