152 ASTHONOMV l\)li lSSi», IfS'JU. 



SUN. 



Rotaiion of ihc sioi. — Mv. Crow, whoso obsorvations of the rotation 

 of the sun wore n<)t<Ml in a i)rovions siiminary, has ma<le a now so- 

 rioa of observations for tho correction or confirmation of his conclu- 

 sion that th(^ anj;iilar velocity of rotation increased with an increase 

 of latitude. Ih^ still finds shorter rotation periods for the highor lati- 

 tudes, tho moan value for the period at latitude 45° being 18 hours 

 shorter than at the equator, though owing to the smallness of this 

 amount ami the uncertainty of the observations he is of theoi)inion that 

 " no certain variation of period with latitude has been detected with 

 the spectroscoj)e." Attention is called however to the wide differences 

 of the ecpiatorial period as obtained by different methods, differences 

 which may be due to the fact that we are really dealing with different 

 strata of tho sun, though here also much reliance must not be placed 

 ui)on the observations. 



Spectroscopic observations made by Dunor for determining the rota- 

 tion time of the sun, confirm the slowing down of the time of rotation 

 with an increase of heliocentric latititudc, quite contrary to the result 

 recently obtained by Wilsing. A i)eriod of U5.4G days is deduced for 

 the sidereal rotation at the equator, and 38.54 days for that at latitude 

 74.SO. 



Diameter of the sun. — r3r. Auwers discusses, in the third memoir on the 

 diameter of the sun, communicated to the Berlin Academy, the observa- 

 tions at Greenwich by Maskelyne and his assistants from 1705 to 1810. 

 Curious ditforoncosof personal equation between different observers are 

 brought out. Instead of Maskely ne's observations giving progressively 

 smaller values of the sun's diameter during his whole observing life, as 

 lias hitheito been supposed. Dr. Auwers's very exhaustive discussion 

 indicates that after tho first two years (which gave a very large value) 

 the observed diameter remained nearly constant for the period 17G7- 

 1772, then during tho years 1772-1790 the diameter was continually 

 <locioasing, lastly irom 1790-1810 the observations gave a diameter con- 

 tinually increasing. Tho minimum value in 1790 was 31'58".i;3 — about 

 \" smaller than the value obtained from modern heliometer measures. 



iSpt>crci\s r<'.sc(()c}u'n on stni .spots.^ Professor Spoerer, who has devoted 

 much altontiou not oidy to tho cunont state of the solar activity, but 

 also to tho early records of sun spots, published early in 1SS9 two im- 

 portant papers on the results of his researches in the latter field. The 

 two i>apers are entitled respectively, Ueber die Periodicitiit der Sonnen- 

 Jlcclcen .seit deni Jdhre 1618, communicated to the Royal Leopold-Caro- 

 line Academy, and iSur leu diffcrenctH <ine prrsentent Vheminpherc nord et 

 riu'misphh-e siid du Soleil, appearing in the number oi' Bulletin Astrono- 

 miijue for February, 1889. The conclusions arrived at in these two 

 l»apers may be summarized under tho three following heads: 



First: Those e.irlior observations afford us many examples of the 

 operation of the "law of zones;" that is to say, a little before a mini- 



