434 Dr. Lamont on the Diurnal Motion of the Magnetic Needle. 



the period to be 10^ years, the maxima would fall upon the fol- 

 lowing: years : — 



1848-5 

 1838-2 

 18175 

 1786-5 

 The agreement with the actual observations is quite satis- 

 factory. 



In order further to show how far the observed increase and 

 decrease agrees with the above hypothesis, I will choose for the 

 period the simplest formula, that is, 



, . / 360°\ 

 a + 6sml c + re T7yr )• 



Assuming, according to the observations in Munich, that a 

 maximum occurred in 1848'5, and calculating the remaining 

 constants from the values obtained at the time of maximum and 

 minimum, we obtain for the magnitude of the yearly motion the 

 following expression, — 



8'-70 + 2'-l sin (72°-58 + w34 c -84), 

 where n expresses the number of years beginning at 1848. Com- 

 paring the magnitude of the diurnal motion calculated from this 

 with the observations before given, we obtain the following : — 



In Gottingen the diurnal motion is y^th greater than in 

 Munich ; deducting this from the results of the Gottingen ob- 

 servations given above, and comparing with our formula, we 

 obtain — 



