^J2i5 







APPENDIX. 



" within a circle of bell metal, divided from the lower 90° 

 each way, as far as fixty-five degrees, into degrees and 

 half-degree s: the other divifions were two degrees and a 

 *' half; the needle being very nearly balanced before it was 

 *' made magnetical : but by means of the crofs D, fixed 

 " on the axis of the needle (on the arms of which were cut 

 very fine fcrews, to receive the fmall buttons cici, that 

 might be fere wed nearer or farther from the axis) the 

 ** needle could be adjufted both ways to a great nicety, 

 *' after it was made magnetical, by changing the fides of 

 ** the needle, and reverfing the Poles. As this needle at 

 ** fea could feldom remain at reir ; to remedy in a great 

 ** meafure this inconvenience, the divided circle is made 

 moveable by turning the button E; fo that when it is 

 ufed at fea, the divided circle is moved till fome prin- 

 " cipal divifion is the mean of the vibrations : then that 

 ** number of degrees and half-degrees diftant from the 

 *' pointer, fubtraded from ninety, gives the dip, if the 

 *' needle is properly balanced : but left it fhould be fome- 

 what out of balance, the moft certain way is, firfl, to 

 take the dip with the face of the divided circle to the Eaft, 

 and afterwards to the Weft, and then changing the ends 

 of the needle by reverfing the Poles, and taking the dip 

 ** as before, with the divided circle fronting the Eaft and 

 ** Weft: and the mean of thofe four dips will be the moft 

 ■** accurate. In each cafe, when the dip is taken, the In- 

 *' ftrument muft be fo placed that the needle vibrates in 

 *' the magnetic meridian." 



2 The 



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