EAKTH'S ACTION ON A NEEDLE. 41 



represented by the action of a blue mass on the north 

 side and a red mass on the south side, or by one of 

 these alone. The result at which we have arrived is 

 analogous in form to that which we have obtained 

 in other magnetical investigations; and, to preserve 

 the analogy of language, we shall call E the Earth's 

 magnet-power. It is important to remark that, on 

 account of the assumed magnitude of c and c', the 

 angular momentum here is expressed by a single term, 

 a multiple of B, without any of the additional terms 

 which occur in Article 20. 



