EARTH'S MAGNETISM PRODUCED BY THE MOON AND SUN. _'.' , 



This enables us to write expression (3) in the form 



= 2 Il/(/>)sm(<r+jo.\'-a'), 

 where 



R/(p) = (-n(n + l) Q/-?9k + . 



Whenp is positive, substituting our expressions for/ p and/',, we timl 



/(p) = 2 



q = 



* r/O ff 



2 (p + 2?) ,, 7 ^ . cos ,* cos ^ . JT 1 , 



fl = 



/ C080^--^,)+g 





Since, in the original equation for R,*(/)), a change in the sign of p only affects the 

 term <rQ n '/sin 8 in the first term, from our last expression we may at once write down 

 the value of B.*( jo), p being positive, by changing the sign of (rQ.'/sin 6. Thus, 



17. For convenience and clearness, some well-known formulae of transformation 

 will now be set down. These have been much used by SCHUSTER in his papers, and 



