•1813.] On the Diurnal Magnetic Declinatio?t. 03 



an apparatus which screened them from the action of the air. 

 The magnet which commuuicated to them the magnetic virtue 

 was in the shape of a horse-shoe, and usually weighed about 

 four pounds. 



Exper. I. 



I took a new needle, on which no magnetic experiments had 

 been made, and converted it into a magnet in the ordinary way, 

 by the double and single touch. It exhibited the small horary 

 variations of the ordinary needle. I took a second needle, 

 perfectly similar to the first ; but instead of communicating to it 

 magnetism in the usual way, I placed the south pole of the 

 magnet on the middle of the needle, and drew it ten times to 

 one of the ends of the needle without returning back again. £ 

 then drew it in the same way ten times towards the other end; 

 and then by means of a small sensible needle determined the 

 poles of this long needle, to which magnetism had been commu- 

 nicated in the peculiar way just described. Its two ends were 

 north poles ; the middle was a south pole (as might have been 

 foreseen from the manner of communicating the magnetic 

 virtue). A more attentive examination presented the following 

 disposition of its magnetism : — 



o — m o 

 + m < ■ > + m 



This needle underwent a daily variation of 40 or 50 minutes, 

 and even of 60 minutes, when the sky was serene ; while an 

 ordinary needle varied only 10 or 12 minutes per day. In 

 February it move? towards the east at nine in the morning, and 

 in the beginning of April at half past seven in the morning. It 

 moves towards the west between two and three in the afternoon, 

 and with such n.pidity as to alter 8 or 10 minutes in an hour. 

 From three to nine it inclines again towards the east, and then 

 returns again towards the west. Hitherto I have observed these 

 variations to be greatest when the sky is serene, and smallest 

 when cloudy or rainy. I have repeated the experiment with 

 various needles treated in the same way, and have always 

 obtained the same declination. 



Exper. II. 



I took another needle similar to the former. I placed the 

 south pule of the magnet upon its middle, and drew it ten times 

 to the extremity of the needle inclined towards the north, while 

 the other half of the needle remained untouched. This, of 

 course, was the same kind oi operation as the preceding. The 

 needle, m before, exhibited great daily oscillations! An attentive 



