140 



A. TAXAKADATE. 



Comparing those variations with the coefficients of the lirst 

 term of harmonic expansion we observe that the agreement is 

 fairly close. It is interesting to remark that even from surveys 

 made over so small portions of the earth surface, we can see 

 where the principal origin of the terrestrial magnetism lies, that 

 is in Gauss's sense. 



Gausses Circuit. 



Gauss in his classical example of the Göttingen-Milan-Paris 

 circuit, might have gone a step further and found those varia- 

 tions approximately. Taking his data and reducing to c. g. s. 

 units we have 



^ Arhitrary 



À ç> o a H unit>. 



Göttingen 9° 58' 51° 3-2' 18° 38' -67° d6' 17813' =0.50983 



3Iilan 9° 09' 45° 28' 18° 33' -G3° 49' 19949 '=0.57094 



Paris 2° 21' 48° 52' 22° 04' -G7° 24' ISlOP =0.51804 



Whence the rectangular components are 



X 



16880' 



Göttingen 



Milan 18913 



Paris 16775' 



which give uniquely 



.5692' 



6347' 



6800 



-43942' 

 -40572' 

 -43485' 



X = 17522.8 + 137.7 J/ - 353:7 J^ 

 Y= G279J- 112.9 J;.- 92'.7J^ 

 Z = -426G6!3 + 141.3 J/- 574!.5J^ 

 where J;>=(;.-7°.16)°E., Jçc=(^-48°.62)° expressed in degrees. 



