THE INTENSITY OF TERRESTRIAL MAGNETISM. 267 



observed in them in preceding years. Part 1, Plate XIII., repre- 

 sents the changes of the Intensity in the upper line, and of the 

 Declination in the lower. The justice of the remark, in p. 259, 

 will be at once recognised, namely, that, when considerable 

 changes take place in the one element, they ar usually accom- 

 panied by considerable changes in the other. Part 2 represents 

 the changes of both elements united in one cm*ve, and affords 

 an illustrative deUneation of the variation of the horizontal por- 

 tion of the earth's magnetic force. To avoid the confusion 

 arising from too repeated involutions of the cvirve, it is divided 

 into three separate portions, and in each of these half the curve 

 is drawn in an unbroken line, and half in a dotted line. 



M. Gauss remarks, that " the observations during this term of 

 Nov. 13-14 do not present greater disturbances than had been 

 noticed in many of the terms at other seasons of the year. On 

 the preceding and following evenings, very great and rapidly- 

 varying changes took place in the declination; but these are 

 known to be the general accompaniments of the Aui'ora Borealis, 

 which was extremely brilliant on those two nights." — Edit.] 



