ON COMPARISON AND REDUCTION OF MAGNETIC OBSERVATIONS. 215 



elimination of non-cyclic element), + being to west of mean. 



ial Force (after elimination of non-cyclic element). 



night, entailing two unmistakable maxima of westerly declination and two 

 of easterly in the twenty-four hours. This accords generally with conclu- 

 sions I., II., III. for Dublin on pp. 175, 176 of Dr. Lloyd's ' Treatise.' His 

 further conclusion, IV., that ' in summer the westerly movement during the 

 night disappears,' is in more doubtful accord with the present results. 

 The variation during the night in summer is so very slow that a definite 

 conclusion would require the warrant of more data than are here avail- 

 able ; but according to Table III. there is, to say the least of it, the 

 suspicion of a slight secondary westerly movement in most of the summer 



