V. 



On the method of com^titing the Dip of the Magnetic J\\edle in 



different latitudes f according to the theory of Mr, JBiot, 



BY NATHANIEL BOWDITCH, LL. B. 



N article upon the '^ Variatious of the Terrestrial Magae- 

 i different latitudes," published in vol. 22 of Tillocb's Philo- 



phical Magazine for the y 



the formulas dis- 



M 



and II 



with 



a 



considerable degree of accuracy all the observations of the Dip of 

 the Magnetic Needle that have been made in various parts of the 



w ■ 



worldy particularly in the northern hemisphere. 



-■ Y 



ject is continued in another paper in the 49th volume of the same 

 work for the year 1817^ in which there is a small alteration in the 



The 



sub 



formula; but the method may be yet considerahly 



plified 



will be shown in the present paper, in which I shall briefly men 

 tion the principles of Mr. Biot's theory^ his formulas^ and the ini 

 provement of which those formulas are susceptible. 

 According to this theory there are 



two magnetic poles P, jp, upon the 

 earth's surface, the northern in the lat- 

 itude of 78^ N, and in the longitude of 

 25° W. from Paris nearly ; the south- 

 ern in 7to° S. and 1.^5° E. nearly. The 



line Pj3 joining these two poles is cal- 

 led the magnetic axis. The plane P Ep 



