OF FERRUGINOUS BODIES. 213 
beautifully imitated. But I have not, at present, 
any spare time to devote to this interesting sub- 
ject ; I must, therefore, content myself, till some 
more favourable opportunity presents itself, with 
having called the attention of philosophers to this 
novel mode of investigation, being perfectly aware 
that there yet remains a rich harvest for those 
who may venture on the pursuit. In conclusion, 
I would beg permission to state, that the expan- 
sions and contractions of the magnetic axis, as 
shown by experiments 23, 24, 25 and 26,* appear 
to me to afford sufficient data for supposing that 
the terrestrial magnetic axis suffers similar muta- 
tions by the direct action of the sun, and that the 
phenomena of diurnal variation, and change of 
intensity on the needle, are probably traceable to 
these secondary causes. 
“ Should these conjectures be correct, there is 
not only a cause of translation of the terrestrial 
magnetic poles, but also a cause of sustentation. 
The sun’s heat may, possibly, be the primitive 
cause of both: directly, the cause of translation ; 
and, through the intermediate agency of electri- 
city, indirectly the cause of sustentation.” 
* Annals of Electricity, Magnetism, and Chemistry, vol. 
iv. Pp. 152, 153. 
Gs 
