t time is a very elastic element in Geology and
Prophecy. If Daniel's seventy weeks mean four hundred and ninety years,
as the learned Prideaux and others have settled it that they do, the
"not many years" of my prediction may be stretched out a generation or
two beyond our time, if necessary, when the prophecy will no doubt prove
true.

It might be fitting to add a few words with regard to the Essay on the
Contagiousness of Puerperal Fever. But the whole question I consider
to be now transferred from the domain of medical inquiry to the
consideration of Life Insurance agencies and Grand Juries. For the
justification of this somewhat sharply accented language I must refer
the reader to the paper itself for details which I regret to have been
forced to place on permanent record.

BOSTON, January, 1861.

A SECOND PREFACE.

These Lectures and Essays are arranged in the order corresponding to
the date of their delivery or publication. They must, of course, be read
with a constant reference to these dates, by such as care to read
them. I have not attempted to modernize their aspect or character in
presenting them, in this somewhat altered connection, to the public.
Several of them were contained in a former volume which received its
name from the Address called "Currents and Counter-Currents." Some of
those contained in the former volume have been replaced by others. The
Essay called "Mechanism of Vital Actions" has been transferred to a
distinct collection of Miscellaneous essays, forming a separate volume.

I had some intention of including with these papers an Essay on
Intermittent Fever in New England, which received one of the Boylston
prizes in 1837, and was published in the following year. But as this
was upon a subject of local interest, chiefly, and would have taken up a
good deal of room, I thought it best to leave it out, trusting that
the stray copies to be met with in musty book-shops would sufficiently
supply the not very extensive or urgent demand for a paper almost half a
century old.

Some of these papers created a little stir when they first fell from
the press into the pool of public consciousness. They will slide in very
quietly now in this new edition, and find out for themselves whether the
waters are those of Lethe, or whether they are to live for a time as not
wholly unvalued reminiscences.

March 21, 1883.

PREFACE TO THE NEW EDITION.

These Essays are old enough now to go alo