506 L. A. Bauer — Wilde's Explication of the Secular 



secular variation expressions given in Prof. Schott's paper, 

 App. 7, Coast and Geodetic Survey Eeport for 1888. Where 

 the curve extends beyond the recorded observations, it is given 

 in dashes. It is well known that the sine periodic function is 

 well adapted for expressing the secular variation. Such a 



function enables you to deduce the period, range, times of 

 maxima and minima, etc. How closely it can be made to agree 

 with actual fact is indicated in the case of the Paris curve, by 

 dots which represent the observations. Here we have the long- 

 est and best discussed series, the earliest observation dating 

 back to 1541, over 350 years ago. The next best discussed 

 series is for Christiania by Prof. Weyer. 



