378 Mr Watfs Description of a new Instrumentjbr 



ridian line ; and, consequently, tlie space between the bars of 

 wood, at the other ends of the instrument, (which serve as indi- 

 ces) is contracted. And when the magnetic force is diminished, 

 the magnets are again attracted toward the magnetic meridian, 

 and the space between the indices is increased. 



1 have observed the indications of an instrument constructed 

 on these principles for nearly a year. The wooden bar, into which 

 an agate capsule was fixed, was four inches long, one inch pro- 

 jected beyond the capsule, to which a light magnet, made of a 

 piece of the mainspring of a watch, was affixed, two and a-half 

 inches long, and balanced by a sliding weight at the other end 

 of the wooden bar. Two of these magnets made exactly simi- 

 lar, with their wooden bars, were placed on two steel pivots, fixed 

 to a stand at the distance of two and a-half inches ; and a scale 

 of degrees having been placed beneath the extremities of the 

 wooden bars which move on the pivots, the general mean result 

 has been as follows. 



The number of the degrees refer to the space contained be- 

 tween the extremities of the bars of wood the degrees were one- 

 twelfth of an inch each. The instrument was placed under a 

 glass shade. 



May 1 November 11 



June > 7 varying to 8° December 12 V varying to 14' 



] 



August 71) February 11 "J 



September 8 VvaryingtolT March 9 vvarying to 10" 



October 9 ) April 9 j 



July } January 12 



Besides this very great annual variation in the magnetic inten- 

 sity, there was, during the spring and summer seasons, a daily 

 variation of a degree, and in winter one-half a degree in clear 

 weather And, although the annual variation was developed 

 as 1 expected, increasing and diminishing in coincidence 

 with the sun's altitude and declination, yet the daily vari- 

 ation was quite the opposite of what I supposed would take 

 place ; for the magnets stood a degree nearer each other from 

 12 m. till 4 p. M. ; and, consequently, the indices which stood 

 at T during the whole summer all the rest of the 24 hours of 

 the day, extended to 8° between 12 and 4 or 5 p. m. I expect- 

 ed, on the contrary, they would have contracted to 6% as the 

 magnetic intensity is greatest during these hours. But this phe- 

 nomenon arises, I conceive, from the mechanical influence of the 

 magnetic current, which, there is every reason to believe, moves 



