— 240 — 



ilisturbance iiifluence, to whicli the eartli is exposed, does 

 uot vary. 



The daily Field. 



In order to ol)tain a representation of this field it is best 

 to distribiite the successive hoiirly values of the componeiits 

 of a certaiii iiumber of stations, sitnated on different parallels 

 along these parallels and to draw the lines of equal vertical 

 component tog'ether with the horizontal vectors. 



Parallels must be taken with regard to the axis of disturhance. 



It is obvious that the features of the system of lines of 

 equal vertical component will suffer strongly from local 

 deviations from the general type of inequality pertaining to 

 the region in which the station is sitnated. For instance, 

 if to the vertical components of the stations: Kingua Fjord, 

 Cape Thonhen, Jan Ma>ien and Sodanki/la' , which exhibit one 

 and the same type of inequality, are added those for Poinf 

 Banoir and Bot^^ehop, where it is quite the contrary, those lines 

 of equal vertical component will a((iuire a queer aspect, wholly 

 useless for onr aim. This aim is the knowledge of the causes 

 of the phenomenon, and to reach it, a representation of the 

 tield exhibiting only the chief characteristic features free from 

 local deviations is required. The investigation of local deviations 

 is of later care; for the present the knowledge of the existence 

 of important deviations may be considered to be sufficiënt. 



Of course we may suppose the field to change during one 

 rotation in such, a degree, that it should be necessary to 

 derive a representation of it for each liour, but the agreement 

 between most of the vector-diagrams (the two stations: Point 

 Barrow and Bossekop included) points tö the contrary. 



In the same mainiej" as for the representalion of his daily 

 field of solar-diurnal inequality Schustkh ') selected a small 

 number of stations sitnated on parallels already known as 

 critical for the phenomenon, in our case those stations have 



1) Philosophical Tranndctioiis 180. p. 4<)7, 



