C44 MAGNETIC AL OBSEKVATIONS. [aPP. N** IX. 



needle is influenced, be not greater near the magnetic 

 pole than it is in England. If it be equal, the oscil- 

 lations of the same dipping needle would be perform- 

 ed, circumstances as to temperature and local attrac- 

 tion being the same, in equal spaces of time in both 

 places ; but if the magnetic power in either place be 

 greater, the oscillations of the needle would there be 

 quicker. 



b. The immber of vibrations of a horizontal needle, per- 

 formed in a certain space of time in Greenland, is to 

 the number performed in an equal space of time in 

 England as 5 to 6, each longer vibration in England 

 being performed in five seconds, and in Greenland in 

 six. No alteration was observed as to the time re- 

 quired for each vibration, whether the temperature 

 was high or low, but I think in a low temperature the 

 vibrations performed by the needle before it stopped 

 were fewer.. 



(c.) The time of oscillation of the same dipping needle, un- 

 der different degrees of magnetic force, appears to me 

 to be reciprocally proportional to the square root of 

 the magnetic force ; or the square of the number of 

 oscillations performed in a certain interval of time, will 

 be directly proportional to the magnetic intensity. 

 .Now, from the observations of Captain Sabine " On 

 the intensity of the Magnetic Force,'' (Phil. Trans. 

 1819, p. 132.), it appears, that the times in which 

 100 vibrations of a dipping needle were made in dif- 

 ferent situations, during the late voyage of Captain 

 Ross, were as follows : 



