146 Mr Barlow's Remarks on the Dip and Intensity of the 



equilibrio in this position by two forces, one directed towards the 

 polar parts N, and the other towards the equatorial parts C. Now, 

 conceive the actual temperature of the several regions to be restor- 

 ed, then all the parts between L and C will be increased in tempe- 

 rature ; and, therefore, according to our supposition in magnetic 

 intensity, while the intensity of all the parts between L and N 

 will decrease, and the needle will, in consequence, be more in- 

 flected towards the centre C ; that is, the dip will be increased : 

 but the actual intensity, independent of the dip, will be greater 

 or less, according as the mean temperature shall be now greater 

 or less than the uniform temperature first supposed ; however 

 this may be, in this particular latitude, there is, at least, some 

 part in which the mean temperature shall be less than the uni- 

 form temperature, and beyond that point, towards the pole, the 

 intensity of the needle will be less, from considerations of tem- 

 perature only, than ihat given by the formula I = u - — . g - 



' 4— 15 sin y. 



it will also be less, because the dip will itself be greater than 

 that which results from the principle upon which tlie for- 

 mula is obtained. It follows, therefore, that, in every mag- 

 netic meridian, there is a point beyond which, towards the 

 pole, the actual observed intensity of the needle will be con- 

 siderably less than ought to result from the formula given 

 by Dr Young, and employed by Captain Sabine; and, in 

 a similar way it may be shewn, that there is another point in 

 each meridian towards the Equator, in which the intensity is 

 considerably greater than that given by the formula; first, in 

 consequence of an increased temperature ; and, secondly, in 

 consequence of an actual diminution of the dip below that due 

 to an uniform temperature. That this would be the actual re- 

 sult due to the magnetic action of an iron ball, heated as we 

 have supposed, is unquestionable ; and the circumstance of such 

 a law being observed in the different zones of the earth, and 

 particularly the proof furnished by Lieutenant Foster's experi- 

 ments, that the solar rays have a positive influence on the mag- 

 netism of the terrestrial sphere, and an influence, moreover, of 

 that kind, which is perfectly consistent with these suppositions ; 

 we have, I think, strong reasons for concluding, that the par- 



