ASTRONOMY. 



157 



lation Hercules. By combining bis results witb tbose of otber astrono- 

 mers, Struve adopts for tbe mean a displacement of about 5", corres- 

 ponding to a velocity of 15 miles per second. The point toward which 

 the system is moving' is still in Ilercnles, right ascension 2GC<^.7, decli- 

 nation -foJo.O. 



The following- table shows how the various determinations of these co- 

 ordinates agree : 



W. Ilersclul. 



Do..-. 



Gauss 



Ar<;el;iu<l('r . 



Liiudabl 



O. Striivo . .. 

 Giillowav - •- 

 Mildk-r .*..... 



Airy 



Dniikin 



GyJdou 



Do.... 

 L. deBall... 



Kane- ken 



Kisfliof 



Ubajjli.s 



L. Stniv(! - .. 

 riuuiiiicr 



Do.... 



D. 



200. (; 



259. 2 

 259. 9 

 '2.->-2, 5 

 261. 5 

 2()0. 1 

 2()1.C> 

 261.5 

 263. 7 

 273. 9 

 260. 5 



269. 

 284. () 

 2H5. 2 

 2()2. 4 

 27.3. 3 



270. 1 

 276.1 



+26. 

 +40. 

 +30. 

 +32. 

 + 14. 

 +37. 

 +34. 

 +39. 

 +24. 

 +25. 



+23. 

 + 31. 



+48. 

 +26. 

 +27. 

 +20. 

 +26. 



Epoch. 



1792. 5 



1792. 5 



1790 



1790 



ISOO 



1800 



1800 



1800 ? 



1800 



1860 



1855 ? 



1855 , 



1810? 



1805 



For the magnitude of the motion in a century we have — 



O. .Striivc 4."31 



Dmikiii .5. 22 



L. SlTuvo 4. 3G 



Gyld^ii 6. 80 



Do 5. 89 



as seen from a star of the sixth uuignitude. 



No. of 

 stars. 



390 



147 



392 



78 



2, 163 

 113 



1,1*37 



(?) 



(?) 



67 



106 



480 



464 



2, 509 

 274 

 274 



SUN, 



Rotation time of the sun. — Mr. Crew, of Johns IIoi)kins University, 

 has made a new determination of the time of revolution of the sun on 

 its axis by comparing the wave-lengths of certain lines in tbe spectrum 

 when measured in light coming from two opi)Osite limbs of the sun. By 

 ])oppler's principle the wave-length of the line in light from the ap- 

 proaching limb ought to be shorter than in the light from the receding 

 limb. The results obtained give a velocity of the photosphere at tbe 

 sun's ecpiator of 2.137 miles per second ; from this the rotation time is 

 determined to be 25.8S days. Mr. Crew's observations indicate an in- 

 crease in the angular velocity of the surface with increase in the helio- 

 graphic latitude. This result is opposed to that obtained by Carriugton 

 and ypoerer from observations oC sunspots. 



