DEPARTMENT OF MERIDIAN ASTROMETRY. >245 



The displacement varies in amount with the separation of the lines, 

 though for all separations it is greater when the companion line is 

 toward the red than when it is toward the violet of the line. This is 

 well illustrated in table A. The subscripts indicate the number of 

 lines included in each mean. For a mean separation of 0.22 a the dis- 

 placements are respectively 0.007 a and 0.005 a. These facts are in 

 accord with the requirements of the theory of JuUus, and they seem 

 definitely to estabHsh the operation of anomalous dispersion in the sun. 



Table A. — Means — Displacement according to separation jrom companion. 



Lines with- 



Separation. 



! 0.0 to 0.2 A. 



Companion toward the red j +.0103ii 



Companion toward the violet | — .007324 



0.2 to 0.4 A. 



+ .0065i7 

 -.002431 



0.4 A and 

 greater. 



+ .0036io 

 -.OOIO9 



Additional results and conclusions are: 



(1) A method is developed bj" which Rowland's Preliminary Table of 

 Solar Spectrum Wave-lengths is made available for comparison of 

 solar wave-lengths with the best recent laboratory wave-lengths. 



(2) The Mount Wilson classification of spectrum lines according to 

 behavior under pressure is confirmed. 



(3) It was shown that the pressure in the solar reversing layer where 

 the Fe Fraunhofer lines originate is 0.5 atmosphere. 



(4) As a direct consequence of the progressive variation in intensity 

 of lines in stellar spectra — ^some lines gradually disappearing and new 

 lines coming in and increasing in strength as we proceed from type to 

 type, thereby causing neighboring lines to change very markedly in 

 relative intensity, some fines gradually losing companions while others 

 gain them — anomalous dispersion becomes one of the causes producing 

 the changes of wave-length which are progressive \vith the stellar 

 spectral type. 



(5) The comparison of the arc wave-lengths of Burns and of Mount 

 Wilson and Pasadena (both of which are of high quaUty) revealed the 

 necessity of stipulating more definite standard conditions in laboratory 

 determinations of wave-length, including standards of wave-length. 



The Director, with Dr. von Flotow, has investigated the pai'allaxes 

 of the large proper-motion stars on the hypothesis of parallehsm of 

 motion toward the apices of preferential motion. In so far as these 

 large proper-motions represent large real velocities of the stars, the 

 hypothetical parallaxes should be very fan* approximations to the 

 truth, for according to the well-estabfished fact of preferential motion 

 the larger motions should be found in the direction of the apices 

 of preferential motion. But the large apparent motions of a consid- 

 erable number of the large proper-motion stars are due to their 



