ON THE PHENOMENA OF TERRESTRIAL MAGNETISM. 
89 
Atlantic. These are the parts of the globe where the principal 
differences take place between the calculated and the observed 
phenomena ; but as the approximation has already been pushed 
sufficiently far to sanction the hypothesis, it is deemed unne¬ 
cessary, and would probably be eventually time thrown away, 
to press to a nearer accordance, until the situation of the four 
points of convergence on the globe has been ascertained, with 
greater precision, by direct observation. 
Since the publication of the Magnetismus der Erde M. Han- 
steen has been engaged in personally determining the lines 
of dip, variation, and intensity, in the North of Europe, and 
throughout the Asiatic dominions of Russia. It is understood 
that he proposes to collect and embody, with the account of his 
own observations which he is preparing, all that has been ac¬ 
complished by others since the early part of the present century; 
and thus to complete, in a second volume, the history of all that 
has been hitherto made known by observation concerning ter¬ 
restrial magnetism. I have deemed it the more proper course, 
as well as that best fitted eventually to advance the inquiry, to 
await this publication from M. Hansteen, rather than to attempt, 
in this year’s Report and with the materials which I now pos¬ 
sess, or which are immediately accessible, the continuation of 
the condensed view which, by the aid of M. Hansteen’s first 
volume, I have endeavoured to give of the results of observation 
in the two preceding centuries. The knowledge of the facts, 
conveyed by a suitably arranged view of what observation has 
made known, is a proper preliminary to an examination of the hy¬ 
potheses proposed either to connect or to explain the phenomena. 
It is a remarkable coincidence, and one of considerable im¬ 
portance towards a correct systematic knowledge of terrestrial 
magnetism, that at the same epoch at which the vicinity of the 
Siberian point of convergence has been visited by an observer 
of M. Hansteen’s experience, furnished with the most perfect in¬ 
struments, the other influential point in the northern hemisphere, 
in the North of America, has been also approached in various 
directions by the British officers employed in North-west disco¬ 
very : and thus the position of the lines of dip, variation, and 
intensity in those two most interesting localities have been al¬ 
most simultaneously ascertained, with an exactness heretofore 
unequalled. Those who have engaged in the endeavour to re¬ 
duce to a common epoch observations made at intervals of time 
apart, can best appreciate how much of otherwise inevitable un¬ 
certainty is removed, when materials which should be rendered 
strictly relative to each other for the purpose of combination. 
