268 S. Newcomb and E. S. Holden on the Periodic 
Art. XXIIL.—On the Possible Periodic Changes of the Sun's 
Apparent Diameter ; by Simon Newcoms and Epwarp §. 
HOLDEN. 
THE question whether the sun’s apparent diameter is subject 
to any changes which can be detected by observation, is one 
which has frequently engaged the attention of investigators. 
In 1809, von Lindenau examined the Greenwich observa- 
periodicity in the observed values of the solar diameter, and 
since that time, the generally accepted conclusion has been, 
that the figure of the apparent solar disc was circular and its 
diameter constant. 
In Gould’s Astron. Journal, iii, p. 97, Winlock has given @ 
discussion of the Greenwich observations of Bradley, and in 
the course of the investigation the varied personal errors of 
various observers are obtained for the first time. : 
It is to be noted, moreover, as a point in the history of this 
question, that Bianchi (Astr. Nach., No. 218, bd. ix, col. 366) 
rediscussed this subject (1831), apparently without a knowledge 
of Lindenau’s research, and that he found the solar compres- 
sion to be z1,. By different combinations of his data, he, 
however, obtained values for this quantity varying from jy's5 
O +10: 
Le Verrier (Annales de I’ Obs. de Paris, tome iv'’™, p. 69) 
also examined this question, and by a process, which he merely 
indicates, arrived at the conclusion that no real variation in the 
sun’s diameter so great as 08-02 was likely to exist. 
Since that time the question has not been directly discussed 
until it was raised by Secchi, whose observations and conclu- 
sions have lately received thorough and searching examination 
by Auwers (Monatsberichte der k. Akademie der Wissenschaflen 
zu Berlin, May, 1873). As the date of this is so recent we shall 
