needle in different parts of' the Northern Hemisphere. 147 



tial intensity of magnetism, in different parts of the globe, is de- 

 pendent on the partial temperature ; and, that the formula de- 

 duced from a supposition of a uniform temperature, will give a 

 less intensity towards the equator, and a greater intensity to- 

 wards the poles, than is consistent with the actual state of terres- 

 trial magnetism ; or, which is the same, the observed intensity 

 in the torrid zone will be found to exceed, and that in the frigid 

 zone to fall short of, the intensity which ought to result from 

 the formula generally emptoyed. And this is consistent with 

 the observations of Captain Sabine, as will appear from the ab- 

 stract we have niade in a subsequent page. In the above rea- 

 soning we have supposed an uniform temperature in each paral- 

 lel of latitude, but this, of course, is by no means the case on 

 the terrestrial globe ; consequently, although the hypothesis ad- 

 vanced above may explain, on general principles, many of the 

 apparent anomalies observed by Captain Sabine, it cannot be 

 expected to meet them entirely ; because, if temperature has the 

 general influence we have supposed, it must also have that partial 

 influence, which is due to localities, and other causes of partial 

 temperature, and hence, perhaps, we may account for that extra- 

 ordinary intensity which Captain Sabine observed at New York, 

 and along the coast of America generally ; the land and ocean 

 furnishing not only different degrees of temperature in the same 

 parallel, but also different conducting powers, and it is probable 

 that much depends upon the latter condition ; and hence, again, 

 perhaps considering the land of the terrestrial globe, as divided 

 into two great continents, we may see some reason why the laws 

 of magnetism, as actually observed on the earth, should be 

 rather consistent with the hypothesis of two north and two 

 south poles, (as first advanced by Dr Halley, and supported by 

 so many authorities by Professor Hansteen), than with that 

 which supposes only one pole in each hemisphere. 



Unfortunately, Professor Hansteen has mixed up, with many 

 valuable records, collected with great labour, a great deal of 

 mystical matter relating to numbers and periods, which have 

 thrown some discredit upon the performance ; but, rejecting the 

 latter, it is extraordinary how very nearly his calculations ap- 

 proach to observations not only as relate to the dip and varia- 



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