62 ON MAGNETISM. 



bar. Let <f> be the mean of the angles thus obtained. 

 Then, referring to the formulae in case (6) of Article 20 



Fig. 27. 



and in Article 21, we shall, as in last Article, obtain the 

 equation 



To this point, the observations, to which this Article 

 and the last refer, appear to throw little light on the 

 subject : but a variation of the experiment, described in 

 the next Article, will give very great information. 



28. Experimental determination continued. Each 

 of the preceding operations performed with the needles at 

 different distances. Reference to numerical observations. 

 The discussion of the first process alone, the discussion of 

 tJie second process alone, and the comparison of the two 

 processes, shew independently that the attraction or repul- 



