H. Crew — Rotation of the Sun. 



155 



July 16th, 1887. 





June 18th, 1887. 





Spectrum of 4th order ; line, 



E 2 ; 



Spectrum of 4th order, line, 



B2 



"Width of spectrum, 2 ,nm ; 

 Definition, good: 





Width of spectrum, 2£ mm 

 Definition, fair; 





Half angle between plumb line and slit, 

 at l h 02 m =24° 30' 



Half angle between plumb line and slit, 

 at 10 h 39 m =29° 54' 



at l h 44 m =37° 00 





at ll 1 ' 53 m = 3° 36' 



Readings on micrometer were 





Reading on micrometer were 



begun at l h 29 m 





begun at 10' 1 59 m 



ended at l h 40 m 





ended at ll 1 ' 14 m 



Micrometer reading. 



Di 



splacement. 



Micrometer reading. 





Eastern 

 limb. 



w 



estern 

 imb. 



Eastern 

 limb. 



Western 

 limb. 



Displacement 



rev. 

 17-698 



17 



rev. 

 777 





0-079 



rev. 

 17-147 



rev. 

 17-231 



0.084 



•710 





779 





69 





187 



•267 



■080 



•719 





799 





80 





208 



•276 



•068 



•692 





774 





82 





212 



•284 



•072 



•718 





799 





81 





196' 



•266 



•070 



•716 





797 





81 





191 



•273 



•082 



•701 





760 





59 





212 



•290 



•07S 



•692 





765 





713 





204 



•293 



•0-89 



. -673 





726 





53 





212 



•283 



•071 



•675 





742 





67 





211 



•284 



•073 



•682 





762 





80 





212 



■294 



■082 



•661 





719 





58 





218 



•296 



•078 



•656 





739 





83 



•214 



■283 



•069 



•665 















Mean -6899 



•7645 



17-20L8 



17-2785 





r 

 .-.A = 



iV. 



0-0746 







rev. 

 .-.A = 0-0767 





To compute the " latitude of observation," %, for these two 

 sets, we have 



X=ff+P+g 



where f c/= angle between projected image* of plumb line and slit, 



at the mean time of observation. 

 p~ position angle, taken from Secchi's table ; Le Soleil, 



2d Ed., p. 22. 

 q= parallactic angle, tabulated for the latitude of Balti 



more. 



Thus on July 1 6th, at l h 35 m p. M. we have 



g—— 68°-64; p= — 4°-40; ^=+41°-94 



whence j=31°-10. 



and on July 18th, at ll h 0l m a. m. 



#=+39°'90; p=— 5°'26 ; q= — 32°-64 



whence j=2 o, 00, 



* It must be noted that during the micrometer readings the prism was removed 

 for the sake of definition and that, when the prism was in position, the image of 

 the plumb line was rotated throguh twice the angle the prism was turned. 



