108 MR. BARLOW ON THE ELECTRIC ORIGIN OF TERRESTRIAL MAGNETISM. 
Woolwich has been enabled to produce a similar effect with a rectangle of 
bismuth only. 
This important discovery of M. Seebeck brings us therefore, as it were, a 
step nearer to our object, by referring us to the sun as the great agent of all 
these phenomena ; indeed but one link seems wanted to connect together a 
chain of highly interesting phenomena, and thereby to reduce to simple and 
intelligent principles what has hitherto been considered amongst the most 
mysterious laws of nature. 
P.S. I have not in the above article made any reference to the irregularity 
of the magnetic lines on the earth. I have spoken of the law as deduced by 
M. Biot, as if it answered accurately all the conditions required : it is however 
very well known that there are irregularities which it will not reach, and much 
credit is due to Professor Hansteen for the talent and industry he has ap- 
plied in the collection of results, and the reduction of them to principles of cal- 
culation. These discrepancies however are by no means opposed to the fore- 
going view of the subject, but are, on the contrary, rather favourable to it ; 
for if, as is implied in the preceding remark, the development of terrestrial 
magnetic phenomena be due to the transmission of caloric and inequality of 
temperature, we ought to expect the same kind of irregularities in this action 
as we know to exist in the temperature and climate of places situated geogra- 
phically the same. 
