C 480 ] 



Tn the foregoing experiments, the needle was 

 railed to an horizontal poiition, and left to vibrate. 

 It was between 8 or 9 minutes before the vibration 

 ceafed. 



The needle brought to an horizontal pofition, and 

 ©ne grain and a half laid on the extremity of the 

 South end, was not fuflicient to keep it in an hori- 

 zontal pofition f but the North end pointed to 

 $5° 30'. One grain and three quarters laid on the 

 extremity of the South end of the needle, was more 

 than fuflicient to keep it in an horizontal pofition, 

 the South end then pointing 6° 45' below o. 



It having been judged proper to have a Drawing 

 of the Dipping - Needle, the following Plate 

 [Tab. XIII.] has been made, wherein 



A A Reprefents the needle. 



B B The ends of the axis refting on the friction- wheels. 



CCCC The four friction-wheels. 



D D D Where flat agate caps are fet in. 



E E E The divided circle of bell-metal. 



FFFF The ends of the crofs for adjufting the needle. 



GG Two levels, whereby the line of o degrees of the inftru- 



ment is fet horizontal. 

 H The perpendicular axis, whereby the inftrument may be 



turned, that the divided face of the circle may front the Eaft 



or Weft. 

 I An index fixed to the perpendicular axis H, and which points 



to an opposite line on the horizontal plate K, when the in- 

 ftrument is turned half round. 

 LLLL Four adjufting fcrews to fet the inftrument horizontal. 



One of them is hid behind the circle. 

 MM MM Screws which hold on the glafs covers, to keep the 



needle from being difturbed by the wind. 



INDEX 



