338 EXPERIMENTS AT SPITZBERGEN. 



The dipping' instrument was one of the usual 

 construction, made by T. Jones, and furnished 

 with polished agate knife-edges, upon which the 

 axes of the needles vibrated. One needle be- 

 longing to the instrument was used solely for 

 the purpose of determining the comparative 

 forces, and its magnetism (which was very uni- 

 form during the voyage) was therefore never 

 interfered with. The force at Shetland is taken 

 at 1*052, which is a mean of the results from 

 the experiments of Captain Sabine, and subse- 

 quent ones of my own near the same place. 

 The variations of the compass were taken, either 

 on shore or on the ice, with Kater's compasses, 

 far removed from any local attraction. 



