388 ANNALS NEW YORK ACADEMY OF SCIENCES 



variable and that it varies with the number of visible sun-spots. He found 

 the diameter of the sun to be greater when the number of spots is a mini- 

 mum, to be smaller when the number is a maximum. In this conclusion 

 he agreed with Secchi, with the observations made at Rome and Palermo. 



DISCUSSION OF MERIDIAN OBSERVATIONS. 



AuwERS. — The results derived by Secchi depended upon a very small 

 number of observations (187), and they covered a period of only one year; 

 yet they attracted considerable attention, and caused Auwers to undertake 

 a complete discussion of the entire matter of the sun's shape and its possible 

 variability. This resulted in a series of papers, published by the Berlin 

 Academy, which are distinguished by their thoroughness and by the great 

 skill of the author. In these papers Auwers clearly shows the utter unrelia- 

 bility of the observations upon which Secchi depended, and concludes that 

 "the assertions concerning variations in the sun's diameter are totally and 

 entirelv unfounded." 



In the first paper of this series,^ Auwers examined a mass of observa- 

 tions made in the years 1871-72, at Greenwich, Neuchatel, Oxford, Wash- 

 ington, Paris, Konigsberg and Brussels, and showed that the different 

 series of observations furnished conflicting results. These series covered 

 the period of time during which were made the observations upon which 

 Secchi relied; and the entire disagreement between the various sets of 

 observations led Auwers to the conclusion that the changes noticed by 

 Secchi were due to "casual errors of observations." The Oxford series 

 showed a distinct relation between the diameter and the sharpness of the 

 image. When the sky was more or less overcast and the image indistinct, 

 the measured diameter was greater. Dividing the observations into five 

 classes, according to the state of the weather, he found the following mean 

 residuals for each class: 



No. OP 

 Class. Residuals. Observations 



Best image — 0».020 1 



Very sharp +0».147 ^ U.i29 (7.) 



Sharp; thin clouds +0».103 3 



Many clouds +0'.237 8) 



Clouds -f0».277 16) U-t'4V-4; 



This dependence of the measured diameter upon the state of the atmos- 



1 Ueber eine angebliche Veranderlichkeit des Sonnendurchmessers, Monatsberichte of the 

 Royal Academy of Sciences at Berlin, May, 1873. 



