480 



SCIENCE. 



[N. S. Vol. I. No. 18- 



meridian. The motion is central, obeying 

 the law of proportionality of times to areas 

 described by the radius vector about the 

 center of the ellipse. 



4. Both the radius and period in the cir- 

 cular 428 days' revolution are systemati- 

 cally variable ; the former between about 

 eight feet and eighteen feet, the latter be- 

 tween about 423 and 434 days ; in a long- 

 period of apparently about sixty-six years. 

 In this inequality of motion the average 

 angular velocity is attained when the size 

 of the circle is least or greatest when the 

 circle has its mean dimensions. 



5. Similarly there are simultaneous 

 changes in the apparent dimensions and 

 velocity in the annual period, which are 

 complementaiy in their character to those 

 in the 428 days' revolution ; but whether 

 they are the result of real changes in the 

 form and dimensions of the ellipse, or the 

 effect of an apsidal motion of long period, 

 cannot at present be determined from the 

 observations available. All that can be 

 said is that observations during five years 

 show that the line of apsides is either fixed, 

 or, if variable, revolving only at a very slow 

 rate. 



6. Besides these two motions of relatively 

 short period, there is distinct evidence of a 

 third motion of rotation in a much larger 

 term, probably not far from twelve years, 

 with a radius of ten or fifteen feet, which 

 reconciles similar indications of slow 

 changes which had been pointed out by 

 other investigators. (A. J., XII., 178; 

 XIII., 35, 36.) 



The results thus established are the out- 

 come of the examination of an immense 

 number of observations, covering the whole 

 interval since the era of refined practical 

 astronomy began, and in fact practicallj' ex- 

 haust the materials which may be drawn 

 for this purpose from existing astronomical 

 annals. The endeavor to make the discus- 

 sion exhaustive in this respect made it neces- 



sary to completely reduce, from the original 

 instrumental readings, extensive older series 

 of observations. It has, incidentally, for 

 example, rescued fi'om almost complete ob-" 

 livion the series of Pond, 1825-36, and 

 sho\\Ti that work to be of a character which 

 will compare favorably with the most re- 

 fined observations made with the meridian 

 instruments of the present daj'. 



Intimately connected with the work on 

 the variation of latitude are five additional 

 papers, containing a redetermination of the 

 value of the aberration-constant from eight 

 different series of observations at the Pul- 

 kowa Observatory, with the prime vertical 

 transit and the vertical circle. The correct 

 value of this fundamental element is one of 

 the most important questions occupj'ing the 

 astronomy of the day. 



VARIABLE STAES. 



The subject of variable stars was erected 

 into a distinct branch of astronomical science 

 \>j Argelander, beginning in 1843, and oc- 

 cupied a large share of his activity and in- 

 terest during a score of years. His classical 

 labors were siicceeded or overlapped bj' 

 those of Schonfeld, who assumed the prin- 

 cipal charge of the subject for another score 

 of years, when his devotion to the great 

 work of the Southern Durchmusterung, and 

 later his failing health, left opportunitj^ for 

 other hands to take up and continue the 

 work where they had left it. Since the is- 

 sue of Schonfeld's Second Catalogue the 

 number of known variables has more than 

 doubled, while the fund of observations per- 

 taining to them has vastly increased. 

 Chandler's work in this direction, besides 

 the incidental work of observation and dis- 

 covery which he has contributed to it, has 

 involved the collection of all the data in 

 astronomical history, their discussion, and 

 the formulation of the elements of their 

 light- variations into numerical laws. The 

 catalogues of 1888 and 1893, while filhng a 



