POOR, THE FIGURE OF THE SUN 



401 



Table V, continued. 



A simple inspection of these figures shows a certain periodicity. This 

 is shown in the series of each observer and in the series of means. The 

 periodic time of these variations is somewhere between six and eight years, 

 and the amplitude about 0".!. The large residual (0".25) for the year 1895 

 is considered by Ambronn to be due to purely personal or accidental causes. 



Ambronn further compares the curves which represent the above series 

 of residuals with Wolfer's sun-spot curve for the corresponding years. This 

 curve, together with the above series of residuals, shows clearly, according 

 to Ambronn, that there is no relation between the observed variations in 

 the sun's diameter and the relative frequency of sun-spots. 



In considering these results of Ambronn, we note that he investigates 

 the possible variation in the average or mean diameter of the sun. The 

 above residuals and the corresponding points on his curves are found by 

 taking, in the series under consideration, the mean for each year of all the 

 observations of both the polar and equatorial diameters. Thus his investi- 

 gation would show whether there had been any change, periodic or secular, 

 in the volume of the sun, and not whether there had been any change in 

 either the polar or the equatorial diameter. Changes in the relative sizes 

 of the diameters of the sun, or changes in its shape which do not alter its 

 volume, could not be discovered by the methods used by Ambronn in this 

 portion of his paper. His conclusions show that, during the entire period 

 of nearly thirteen years, there was not present any periodic or secular vari- 

 ation in the sun's volume larger than that represented by a change of O'M 

 in the mean diameter of that body. 



A comparison of the final values of the sun's diameter as found by Schur 

 and Ambronn, with that found by Auwers from the transit of Venus obser- 

 vations, shows the new values to be considerably larger; but this difference 

 is attributed to instrumental and personal peculiarities. The aperture 

 of the objective, the color and density of the shade-glass used, — each has 



