ASTRONOMY. 



157 



latioii nercules. By combiuin*^ his results witb those of other astrono- 

 mers, Striive adopts for the mean a displacement of about 5", corres- 

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

 the system is niovinj:^ is still in Hercules, right ascension 2G60.7, decli- 

 nation + 31O.0. 



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

 ordinates agree : 



W. Herschel. 



Do..-. 



Gauss 



Arjj;elauder . 



Lundalil 



O. Struve . .. 

 Galloway . .- 



Miidler 



Airy 



Dunkiu 



Gyldeu 



Do.... 

 L. deBall... 



Kancken 



Bischof 



Ubaglis 



L. Struve . .. 

 Plumuier 



Do.... 



A. 



260. 6 

 245. 9 

 259. 2 



259. 9 

 2.52. 5 

 2G1.5 



260. 1 

 261.6 

 261.5 

 263. 7 

 273. 9 



260. 5 

 269. 

 284.6 



285. 2 

 262. 4 

 273. 3 

 270. 1 

 276.1 



D. 



+26. 3 

 +40. 4 

 +30. 8 

 +32.5 

 +14.4 

 +37. 6 

 +34. 4 

 +39. 9 

 +24. 7 

 +25. 



+23. 2 

 +31.9 

 +48.5 

 +26. 6 

 +27. 3 

 +20. 3 

 +2C>. 5 



Epoch. 



1792. 5 

 1792. 5 

 1790 



1790 



1800 



1800 



1800 



1800? 



1800 



1860 



1855? 



1855 g 



1810? 



1805 



No. of 

 stars. 



390 



147 



392 



78 



2,163 

 113 



1,167 



(?) 



(?) 



67 



106 



480 



464 



2, 509 

 274 

 274 



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



O. Stnivo 4."31 



Duiikin 5. 22 



L. Struvo 4. 36 



Gyl.lon 6. 80 



Do 5. 89 



as seen from a star of the sixth maiinitude. 



SUN. 



Rotation time of the sun. — Mr. Crew, of Johns Ilopkins University, 

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

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

 when measured in liglit coming from two opposite limbs of the sun. By 

 Doppler'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 the 

 sun's equator of 2.437 miles per second ; from this the rotation time is 

 determined to be 25.88 days. Mr. Crew's observations indicate au in- 

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

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

 and Spoerer from observations of suuspots. 



