18 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



stances thrown up, as they fall, will produce a region of gen- 

 eral and also selective absorption. When any portion of the 

 descending material is liquid, the general absorption will be 

 great. This will then form the centre of the spot. In follow- 

 ing out their theory, the authors adduce numerous points of 

 detail in which observations sustain their views. Monthly 

 Notices Roy. Ast. Soc, XXXIV., 26. 



THE VARIABILITY IX THE DIAMETER OF THE SUN. 



The investigation of a possible change in the solar diame- 

 ter, coincident with the changes of solar spots, has been re- 

 vived by Wolf, of Zurich ; and, while giving full weight to 

 the conclusions of Wagner and Auwers, he recalls a half-for- 

 gotten work of his own, undertaken many years ago; and 

 shows that, in spite of the negative results arrived at by 

 Ainvers, we are still justified in drawing the conclusion that, 

 at least in Maskeleyne's observations, there are very plain 

 traces of the existence of a solar-spot period, and that Secchi's 

 conclusions are possibly correct, although the basis for them 

 adduced by him w r as quite unsatisfactory. The curves given 

 by Wolf show that, as the number of solar spots increases, 

 the solar diameter diminishes. IVolfs Astron. Mitth., No. 

 34, 134. 



THE VARIABILITY OF THE SUN'S DIAMETER (AGAIN). 



The investigations of Father Secchi, based on the short 

 series of observations made by Father Rosa, and which led 

 him to the conclusion that there was a variation in the sun's 

 diameter coincident with the variations in the spots and pro- 

 tuberances, have led to an exhaustive and valuable article 

 by Dr. Auwers, who shows, first, that Secchi had no good 

 reason to draw his conclusion from the somewhat inaccurate 

 observations of Rosa ; and, furthermore, by an extended in- 

 vestigation of all the observations available, made at other 

 observatories during the same period of time as that em- 

 braced by Rosa's observations, he proves that there is con- 

 clusive evidence as to the non-existence of any variation of 

 the solar diameter at this time, and that the changes noticed 

 by Secchi must have been due to casual errors of observation. 

 Pursuing the subject still further, Auwers has also examined 

 the lono; series of Greenwich observations made since 1750, 



