s are probably aware that the question of the causes of
glacier formation and motion, cool as the subject may seem in itself,
has demonstrated the existence of a great deal of latent heat among
scientific men. In England, the so-called _viscous_ theory of
Professor J.D. Forbes held for a long while undisputed possession of
the field. According to him, "a glacier is an imperfect fluid, or
viscous body, which is urged down slopes of a certain inclination by
the mutual pressure of its parts." With that impartial
superciliousness to all foreign achievement which not seldom
characterizes the British mind, the credit of all the results of
observation and experiment on the glaciers was attributed to Professor
Forbes, who seems to have accepted it with delightful complacency. But
presently doubt, then unbelief, and at last downright opposition began
to show themselves. The leader of the revolt was Professor Tyndall,
whose book is now before us. The controversy has begotten no little
bitterness of feeling; but none is shown in Mr. Tyndall's volume,
which is throughout written in the truest spirit of science,--with the
earnest frankness that becomes a seeker of truth, and the dignity that
befits a lover of it.

Not content with any theoretic antagonism to the Forbes explanation of
the phenomena, Mr. Tyndall devoted all the leisure of several years to
an examination of them on the spot. At the risk of his life, he
verified the previous observations of others and made new ones
himself. At home, he made experiments upon the nature of ice,
especially upon its capacity for regulation and the effect of pressure
upon it. He satisfied himself that snow may be changed to ice by
pressure, that crumbled ice may in like manner be restored to its
original condition, and that solid ice may be forced to take any form
desired. Under proper conditions, lamination may be produced by the
same means. The result of his investigations is, that the glacier is a
solid body, and that _pressure_ answers all the requirements of the
glacier-problem, and is the only thing that will.

The book is one of uncommon interest, and discusses many topics beside
the glaciers, though nothing that is not in some way related to them.
Mr. Tyndall does justice to former investigators,--especially to M.
Rendu, who, though imperfectly supplied with demonstrated facts,
theorized the phenomena with the happiest inspiration,--and to
Agassiz, of whose important observations,