TERRESTRIAL MAGNETISM. 127 



8JA.M. (20 J astronomical reckoning) than at any other hour, 

 making then the nearest approach to the true or geographical 

 north at all places where the declination is westerly. From 

 that hour this end of the needle moves gradually westward 

 until 1} P.M., when it reaches its most westerly elongation. 

 This movement to the westward is general ; it takes place 

 in the same direction at all places in the middle latitudes of 

 the northern hemisphere, whether they have west declination, 

 as the whole of Europe, Pekin, Nertschinsk, and Toronto 

 in Canada ; or east declination, as Kasan, Sitka (in Russian 

 America), Washington, Marmato in New Granada, and 

 Payta on the coast of Peru.( 152 ) Erom the above-mentioned 

 most westerly pointing at If h., the needle returns towards 

 the east during the afternoon and a portion of the night 

 until 12 h. or 13 h., often making, however, a small pause 

 at about 6 h. In the night there is again a small movement 

 to the westward, after which the easterly march is resumed 

 until the most easterly pointing of the needle is attained, 

 which, as already stated, is at 20J h. astr., or 85 A.M. This 

 nocturnal period, which was formerly quite overlooked, a 

 gradual and uninterrupted progression to the east from 

 If P.M. until the morning hour of 8 having been the 

 general belief, strongly engaged my attention at Rome, 

 when I was occupied there with Gay-Lussac in examining 

 the horary variations of the declination with a Prony's 

 magnetic telescope. The needle being generally more 

 unquiet while the sun is below the horizon, this small 

 nocturnal movement to the west presents itself on that 

 account both less frequently and less distinctly to the 

 recognition of the observer. When it does show itself 

 distinctly, I have noticed it to be unaccompanied by any 



