POOR, THE FIGURE OF THE SUN 



423 



Table XVI. 



1897 

 April 19. 



1900 

 Feb. 5 



Sums. 



3 

 &0^6 



+ 1.5752 

 —0.2549 

 —0.2903 

 —0.0217 

 + 0.2213 

 —0.1859 

 —0.5121 

 + 0.0105 

 + 0.5543 



+ 0.2688 

 + 0.0063 

 —0.1188 

 + 0.0543 

 + 0.1251 

 —0.0138 

 —0.0470 

 + 0.0732 

 +0.0544 



+ 1.8440 

 —0.2486 

 —0.4091 

 + 0.0326 

 + 0.3464 

 —0.1997 

 —0.5591 

 + 0.0837 

 + 0.6087 



—0.1348 

 —0.2219 

 + 0.0174 

 + 0.1878 

 —0.1083 

 —0.3032 

 + 0.0454 

 + 0.3301 



The x's pass through two complete cycles in fifty-six days, thus again show- 

 ing the tendency of the observations to group themselves in periods of twenty- 

 eight days. 



The present investigation would appear to show, therefore, that, at the 

 time of these observations, the measured differences between the equatorial 

 and polar diameters of the sun had a decided tendency to fluctuate in a 

 period of approximately twenty-eight days. This would indicate that the 

 sun's equator was deformed; whether this deformation was permanent or 

 transitory, the observations afford no means of deciding. 



Part IV. Conclusions. 



The general results of the present investigation may be summed up in 

 the following: — 



1. The exact shape of the sun is not known. The generally accepted 

 idea that the sun is a sphere is at least open to question. Practically every 

 series of measures heretofore made show departures from a spherical form; 

 but these departures are extremely minute, the difference between the 

 different radii of the sun being probably not more than 0".25. 



2. A study of all the available heliometer measures shows a fluctuation 

 in the shape of the sun corresponding in period with the sun-spot cycle. 

 The amplitude of this fluctuation is small, being probably not over 0".10. 

 This variation is shown by the great mass of heliometer measures made by 

 the German observers in connection with the transits of Venus in 1874 

 and 1882, and by the superb series of observations made by Schur and 

 Ambronn at Gottingen in 1890-1902. 



