18 



Mr Harris on Magnetic Intensity by the 



described (29). The force, as again estimated at each pole by 

 the magnetimeter, was now doubled, and the retarding force on 

 the copper again observed. In this case the latter was also found 

 to be doubled. 



Thefollowing Table comprises the results of this experiment. 



TABLE I. 



Tension by Attraction. 

 Distance of Iron 0.25. 



Tension by Vib. of Ring. 

 Distance of Poles 0,9. 



5° 

 10° 



^-1 = 0.818 



55 



^-1 = 1.681 



DO 



The vibrations of the ring were observed between 40° and 

 30°, between which limits, when vibrating alone, it completed 

 exactly 1 00 vibrations ; and when caused to vibrate about the 

 magnet, it completed 55 vibrations with the lesser tension, and 

 38 vibrations when the tension was doubled. In this instance, 

 the respective forces deduced by the formula, correspond as nearly 

 as could be expected with the previously observed attraction on 

 the iron. 



This method of detecting changes in the magnetic force of a 

 bar, seems therefore susceptible of precision. It is besides ex- 

 tremely delicate ; the only apparent objection is the great accu- 

 racy in manipulation requisite for its perfect success. It is never- 

 theless available at any time, and in any place, since the vibra- 

 tions of the copper-ring alone, taken within certain limits, may 

 be always reduced to a constant and given number. 



31. The experiments of Morichini and Mrs Somerville 

 seem to shew, that certain magnetic properties exist in the solar 



