needle in different parts of the Northern Hemisphere. 149 



greater. It follows, therefore, that the intensity of the hori- 

 zontal needle may be at its maximum, when the general in- 

 tensity is at its minimum, and vice vcrsa^ particularly in places 

 where the dip is very great, because there a very few mi- 

 nutes' change in the dip will very sensibly affect the horizontal 

 needle, while that of the dipping-needle will scarcely have suf- 

 fered any perceptible alteration. Irregularities in the horizontal 

 needle will therefore be much more common, and more appre- 

 ciable, in northern latitudes, than in places near the Equator ; 

 while changes in the state of the dipping-needle will be more 

 common in the latter situations than in the former ; all which I 

 believe is sufficiently consistent with observations ; at least Pro- 

 fessor Hansteen has recently shewn, that the change of intensity 

 in the horizontal needle, between its annual maximum and mi- 

 nimum, is much greater as the dip is greater ; and I think it 

 highly probable, if his observations had extended to places nearer 

 the Equator, he would have found it a minimum in one place, 

 when it was at its minimum in the other. 



It would, however, be endless to trace out all the circum- 

 stances that might result in different places, by supposing that a 

 higher temperature developed a higher degree of magnetic in- 

 tensity. I shall therefore content myself with what is above 

 stated, hoping that it will be sufficient to attract the attention of 

 observers to this probable cause of magnetic irregularities in dif- 

 ferent parts of this terrestrial globe. 

 Woolwich, 1 

 \m May 1827. j 



ERRATUM IN THE FORMER PAPER. 



For Professor I-ieibech read Professor Seebeck. 



Refutation of Mr Ivory's New Law of the Heat extricated from 

 Air hy Condensation. By Mr Henry Meikle. — Commu- 

 nicated by the Author. 



W HEN writing the articles on the relations of air and heat, 

 inserted in the last Number of this Journal, I was not aware that 



