232 CARNEGIE INSTITUTION OF WASHINGTON. 



wave-length is shown by the bolometric work of Abbot and by the 

 observations of Schwarzschild and Vilhger, who photographed a small 

 image of the sun through a silver film transmitting light of X3200. It 

 occurred to the Director that this method, if applied on a sufficiently 

 large scale, might aid in accomplishing two objects: (1) the better 

 detection of the ''faint markings" or minute spots found by Maunder 

 at Greenwich in very high solar latitudes and also of possible faint 

 spots in bipolar groups that appear unipolar in ordinary photographs; 

 and (2) the enhancement of the contrast in the photospheric structure to 

 a degree sufficient to permit better study of the granulation. In order 

 to test the method for these purposes, small plane speculum metal 

 mirrors were figured in our optical shop and mounted on the coelostat 

 and in front of the second mirror of the Snow telescope. A concave 

 speculum metal mirror of 60 feet focal length was also prepared and 

 mounted in front of the large concave mirror. The light from the 

 silvered surfaces of the large mirrors was completely cut off, and the 

 solar image, 6.5 inches in diameter, was thus formed by the light from 

 the speculum metal mirrors, which have a fairly high coefficient of 

 reflection in the ultra-violet. A thin piece of plane glass, found to 

 transmit ultra-violet light of X3200, was silvered on one face and 

 mounted in front of the photographic plate, at a distance of about 20 

 inches. 



Photographs of the photosphere and spots made with this apparatus 

 do not as yet show the increased contrast expected, but the method 

 seems of sufficient promise to warrant further development. 



PECULIARITIES OF THE CENTRAL LINES OF ZEEMAN TRIPLETS 

 IN SUN-SPOT SPECTRA. 



The fact has been mentioned in previous reports that the central or 

 p-component of many sun-spot triplets does not behave as theory and 

 laboratory experience would lead one to expect. When the spectrum 

 of a large spot not too far from the center of the disk is photographed 

 with the Nicol and compound quarter-wave plate, the outer or n-com- 

 ponents of the Zeeman triplets are alternately cut off on successive 

 strips of the quarter-wave plate, while the p-component is transmitted 

 with intensity which varies across the spot. If, as theory and labora- 

 tory experience would indicate, the p-component were plane polarized, 

 it should show no relative displacements on adjoining strips. As a 

 matter of fact, however, it does show such displacements, opposite in 

 sign to that of the n-components. That is, on a strip where the red 

 n-component is weakened and completely cut off, the p-component is 

 slightly displaced toward the red. 



The degree of this displacement and its relationship to the separation 

 of the n-components (which indicates the strength of the field at this 

 level in the sun-spot) have been measured by the Director and Mr. 



