DETERMINATION 



OF 



MAGNETIC CONSTANTS. 



The magnetic constants determined were the horizontal component (H) 

 of the terrestial field and the declination. The dip was not attempted from 

 the want of instrumental appliances. 



DETERMINATION OF H. 



The method of measuring H was essentially that of Gauss, and consisted 

 in determining the product and ratio of H and M, M being the moment of the 

 bar magnet used. We took four bar magnets called A, B, 0, D. A and B had 

 circular sections, and C and D square sections. They were carefully made to 

 fulfil the geometrical conditions as nearly as possible. The following table gives 

 their dimensions at 20° C. 



Ma.gket. 



Length ' 



Diameter or breadth 



Mass 



Moment of inertia .■• 



10.020 cm. 



.805 „ 

 39.684 gr. 

 334.58iQC.gr. 



B. 



7.016 cm. 

 .821 „ 

 28.903 gr. 

 l20.52iDC.gr. 



C. 



10.012.cm. 

 .793 „ 

 50.880 gr. 



D. 



7.988 cm. 



.794 „ 



39.324 gr. 



427.72inc.gr.211.40inc.gr 



In determining their lengths, the bar was brought in contact with an 

 iron scale graduated to -J- mm. and the positions of the ends of the bar were 

 read with a micrometer. Four measurements wore made along different 



