410 



ANNALS NEW YORK ACADEMY OF SCIENCES 



on the same day, nor is the number of polar and equatorial diameters the 

 same in any series. In reducing the observations of any one observer, 

 Auwers took the mean of all diameters measured within 15° of the poles, 

 and called such mean the polar diameter. He similarly took the mean of 

 all diameters measured within 15° of the equator, and called such mean 

 the equatorial diameter. The mean dates to which these mean diameters 

 belong are not given by Auwers. For example, the observations made by 

 Adolph in Strassburg were all made on fifteen days between Sept. 2 and 

 Sept. 25, 1873. In this series Adolph made in all some fifty-seven determi- 

 nations of the sun's diameter; of which fifty-seven measures ten fall within 

 the 15° limit of the pole, and nine within the corresponding limit of the 

 equator. The polar measures were made on Sept. 8, 14, 18 and 21; the 

 equatorial measures, on Sept. 18, 20, 21, 23 and 25. The remaining thirty- 

 eight observations of this series were not utilized by Auwers in this investi- 

 gation. 



As a result of these nineteen measures by Adolph, Auwers finds the 

 value for the ratio between the polar and equatorial diameters — O'MG, 

 in the sense polar minus equatorial; and this value, I have assumed, is the 

 value for Sept. 18, the mean date of the observations. Such an assumption 

 is, of course, more or less approximate, but it gives a date sufficiently close 

 for the purpose in hand. 



Series of 1873-75. — In the first series of observations, extending from 

 1873 to 1875, there are in all thirteen such sets of observations. These are 

 tabulated below, being arranged according to the mean dates of the observa- 

 tions, the weights being those assigned by Auwers. 



Table IX. 



