An introduction to astronomy: designed as a text-book for the use of students in college. By Denison Olmsted ...

PREFACE TO THE REVISED EDITION.
THIS work was revised by its author in 1854, at which time
were introduced notices of the recent discoveries in Astronomy.
The changes made in the present edition are mostly of a different character. While there have been added brief accounts of
still later discoveries, and of new methods of observation, it
has been especially my aim to give more clearness to certain
descriptions and demonstrations, which my experience as a
teacher has shown me to be perplexing to the learner. The
discussion of central forces is entirely remodeled, and the great
law of gravitation throughout the solar system is deduced, by
a more direct and less cumbrous mode of reasoning, from the
three laws of Kepler, which are taken as facts established by
observation.
To those numerous teachers who approve the general design
of Professor Olmsted in the preparation of this work, as set
forth in his preface, and who have themselves tested the utility
of that design, it is hoped that the changes now made will
commend themselves as improvements.
E. S. SNELL.
AmHEasT COLLEGE, March, 1861.