DETERMINATION OF THE MAGNETIC INTENSITY AND DIP, 

 L834-5, is Hi, 1841, AND L843. 



Determination of the Magnetic Intensity. 



A. Relative horizontal intensity by vibrations of a bar (needle A), and of a 



cylinder (needle C). 

 1). Relative total intensity by deflections of Lloyd needles with weights. 

 C. Magnetic inclination. 



Correction for Temperature to the observed Time of Vibration. 



The coefficient of temperature m has been determined by special experiments 

 which, together with the result, are published in the Trans, of the Amer. Phil. 

 Society, Philadelphia, Vol. V. new scries, Part III. 1837, Art. XXVIII. -On 

 the relative borizontal intensities of terrestrial magnetism at several places, b\ A. 

 D. Bache and E. H. Courtenay." 



The bar is called in that paper needle A, and the cylinder needle ('; on page 

 413 the value of the temperature coefficient is stated as follows: — 

 For the bar, m = 0.000117 



For the cylinder, m = 0.000052 



Let T = time of oxidation at temp, t 



ml a a u I' 



then T = T \ 1 - m ((' - t) j 



The above numerical values were used in reducing the time of 10 vibrations to 

 the adopted standard temperature 00° Fahr. 



log /// for the bar, 6.068186 



log m for the cylinder, 5.716003 



( 18 ) 



