Prof. Hansteen on the Aurora Borealis. 
kr lights not appear equally powerful every season, but have 
periods of from 60 to 100 years, during which they display 
themselves with great splendour, after which they have pauses 
of nearly equal length ? When we consider, I say, the appa- 
rent impossibility of answering these questions, in a satisfactory 
manner, on any other hypothesis, and how readily an answer to 
the most of them suggests itself, when we adopt a magnetic orL 
gin to the polar lights, it seems a matter of course to admit this 
hypothesis. Nor is it a new one. All the naturalists who have 
had more than a superficial knowledge of magnetism, and who 
can be considered as competent judges of this subject, have ad- 
mitted it. I Jiave only to mention as the first and chief of these, 
Dr Halley ; and next to him the Swedish naturalists Celsius, 
Hiorter, Wargentin and Wilcke. If any person can explain 
all the external phenomena of the polar lights, by assuming ra- 
ther an elastic material fluid, on portions of which the magne- 
tism, of the earth can operate according to the known laws of at- 
traction and repulsion, there still remains this important ques- 
tion, which our present knowledge of the sciences cannot an- 
swer, What is this material substance ? Is it electricity in a 
neutral state, as we have learned to know it in the insulated gal- 
vanic chain in the experiment of Oersted ? or, Is it an elementary 
substance, in some other state as yet unknown to us, and on 
which the magnetic powers only can act * ? 
( To he continued.) 
Art. XI. — Account of the measures adopted for pulling down 
the Ruins caused hy the late great Fires at Edinburgh^ on 
16^^, and ilth November 1824. Drawn up by a Naval 
Officer present. (With Engravings). 
It is not the intention of this notice to give any description 
of the recent destructive Fires : there was nothing respecting 
them, indeed, possessed of any peculiar interest, more than al- 
ways attends a great catastrophe of this nature. 
* A copious statement of all the known external phenomena of the polar 
lights, together with a historical account of their different periods and pauses, will 
be found in the second part of my “ Magnetismus der Erde^^ if circumstances 
should ever put it in my power to bring this work to light, 
