36 Mr Watt on a New Magnetical Instrument, 



If we simply consider that the south pole of any magnet pos- 

 sesses as great a power of attraction and repulsion as its north 

 pole, that the compass needle diminishes in its variation as it ap- 

 proaches the equinoctial line, and increases both in its annual 

 and daily variation as it advances towards the north pole ; and, 

 after passing a certain degree of latitude, loses its power of ex- 

 hibiting its polarity altogether ; reasoning analogically, we should 

 be led to a conclusion the opposite of that usually held. 



The fact, that the sun in the Arctic Regions produces a more 

 visible and extensive variation in the magnetic needle than in 

 the latitudes near the equator, seems to indicate, that the needle 

 v^fithin the Arctic Circle is more free to move to any incidental 

 impulse, than when near the Torrid Zone ; and we would na- 

 turally be inclined to conclude from this circumstance (nihil 

 contradicente) that it possessed near the Arctic Regions, both 

 less polar attraction and less local, than when near the Equa- 

 tor. 



The observations made by Captain Parry and his officers de- 

 monstrate, that the needle, in its diurnal variations, was influ- 

 enced by the sun, and that the south pole of the magnet was at- 

 tracted to the sun ; the maximum westerly variation of the 

 north pole of the needle having been observed to occur at Port 

 Bowen, between 10^ a. m. and 1^ p. m., and the minimum be- 

 tween 8^ r. M. and ^ a. m. ; and the diurnal variation some- 

 times amounting to 6° and 7°. 



It was likewise discovered, that an increase of magnetic in- 

 tensity was exhibited from the morning to the afternoon, and a 

 decrease from the afternoon to the morning. Captain Parjy 

 farther observed, " that it appeared that the sun, and, as we 

 had reason to believe, the relative position of the sun and moon, 

 with reference to the magnetic sphere, had a considerable influ- 

 ence, both on the intensity and diurnal variation,*" (of the 

 needle)*. 



It therefore appears to me to be perhaps as consonant to ge- 

 neral ol>servation, if not more so, to conclude, that when the 



♦ One of Captain Parry's officers, who was frequently employed in watch- 

 ing the movementa of the needle at Port Bowen, mentioned to me, that he 

 sometimes obseryed a considerable deflexion of the needle just at sun-rise, 

 when the atmosphere was clear. 



