1770 and 1844--Cause of acceleration in the case of Encke--Anomalous
motions of the comet of 1843--Change of diameter at different
distances of a comet from the sun--Cause of this change--Nature of the
nebulosity--Formation of the tail--Compound nature of a comet's
light--motion and direction of a comet's tail--Phenomena presented by
the great comet of Halley--Mass of a comet--The Zodial light--Nebulous
stars--Shooting stars--Periodic showers--Periodicity doubtful--Cause
of the apparent periodicity--Cause for being more numerous in Autumn
than in Spring. 187


SECTION SIXTH.

State of the polar ice since 1845--Sir John Franklin's track--Probable
existence of islands north of Behring's Straits--Possibility of
subsisting in the Arctic islands--News from the
Investigator--Necessity of searching in a higher latitude than the
Investigator visited--Franklin's misfortunes due to Scientific
Errors--Relative levels of the Atlantic and Pacific Oceans--The Arctic
seas more accessible in a few years--Conclusion. 233




PREFACE.


On presenting to the public a work of this novel character,
overstepping, as it does, the barriers erected by modern systems to the
further progress of knowledge, a few words of explanation may not be