POOR, THE FIGURE OF THE SUN 395 



in 1842-43 and 1846-51. The observations were too few in number to 

 allow any certain conclusion to be drawn, but they indicated a change in 

 the diameter. Schliiter also measured on a few days both the polar and 

 equatorial diameters, and, as a result of these measures, the polar diam- 

 eter appeared to exceed the equatorial by a small fraction of a second. 



Measures made in Connection with Transit of Venus. — While 

 adjusting and determining the constants of the heliometers which were 

 used in observing the transits of Venus in 1874 and 1882, the German 

 observers made a great number of determinations of the sun's diameter. 

 In all, some 2692 separate measures of the diameter were made by twenty- 

 three observers. Five heliometers were used, measures with the same 

 instrument being made in various stations by the same observer and in the 

 same station by various observers. Thus heliometer A was used by Adolph, 

 Wittstein, Valentiner, Ambronn, Peters, Kobold, DeichmuUer, Hartwig, 

 Kustner and Weinek in Strassburg; by Adolph and Valentiner in Tschifu; 

 and by Franz and Kobold in Aiken. 



This immense mass of data was most thoroughly discussed by Auwers 

 in "Die Venus-Durchgange, 1874 und 1882"; the conclusions being pub- 

 lished in the " Astronomische Nachrichten." ^ These measures were all 

 reduced to distance unity and arranged in groups, the observations made 

 with each instrument being subdivided for each observer and also for each 

 place of observation. From the observations made with the different 

 heliometers, Auwers reached the conclusion that D and E gave smaller 

 images than A, B and C, and he deduced corrections for the five instruments, 

 so as to reduce the measures made with each to the mean of A + B + C + 

 D + i E. These corrections are given by the table. 



For A — 0".01 ForD +0".18 



ForB — 0".20 For E +0".16 



ForC — 0".06 



With these corrections the observations were reduced and the results 

 for the various observers tabulated. The observations of Hartwig made 

 the diameter the greatest, 1920".29, while those of Clauss made it the least, 

 1918".38: the difference between these two observers thus amounted to 

 1".91. To these various means Auwers assigned weights, and finally 

 deduced the value for the diameter of the sun at distance unity as 



1919".26 ± 0".10. 



1 Astronomische Nachrichten, Vol CXXVIII, No. 306S, December, 1891. 



