518 
ON THE DIURNAL VARIATION OF TERRESTRIAL MAGNETISM. 
the manner explained by Professor Schuster. The fanction actually computed by 
Professor Schuster in Tables XXII. and XXIII. is the ratio 
which 
cl 
ch 
\ (tl/i + 
-M-l) 
(Ir 
_ {'!'>' + 1 ) X» _ 
/.;R:^,/(Mt) + (71 + i)y„(/,ao' 
For large values of S, i.e. for sufficiently small values of p, we may put 
cosh ^ = sinh whence, keeping only the most important term in [Q, the fraction 
written becomes 
= + = 
The difference of phase therefore tends to the limit 45°, as remarked by Professor 
Schuster. For 8 = 100, this formula gives for the reduction of amplitude the value 
'3 and '5 in the cases n = 2 and n = A respectively. 
