YALE UNIVERSITY MRS. HEPSA ELY SILLIMAN MEMORIAL LECTURES In the year 1883 a legacy of eighty thousand dollars was left to the President and Fellows of Yale College in the city of New Haven, to be held in trust, as a gift from her children, in memory of their beloved and honored mother, Mrs. Hepsa Ely Silliman. On this foundation Yale College was requested and directed to establish an annual course of lectures designed to illustrate the presence and providence, the wisdom and goodness of God, as manifested in the natural and moral world. These were to be designated as the Mrs. Hepsa Ely Silliman Memorial Lectures. It was the belief of the testator that any orderly presentation of the facts of nature or history contributed to the end of this foundation more effectively than any attempt to emphasize the elements of doctrine or of creed; and he therefore provided that lectures on dogmatic or polemical theology should be excluded from the scope of this foundation, and that the subjects should be selected rather from the domains of natural science and history, giving special prominence to astronomy, chemistry, geology, and anatomy. It was further directed that each annual course should be made the basis of a volume to form part of a series constituting a memorial to Mrs. Silliman. The memorial fund came into the possession of the Corporation of Yale University in the year 1901; and the present volume constitutes the fourteenth of the series of memorial lectures. SILLIMAN MEMORIAL LECTURES PUBLISHED BY YALE UNIVERSITY PRESS ELECTRICITY AND MATTER. _By_ JOSEPH JOHN THOMSON, D.S.C., L.L.D, PH.D., F.R.S., _Fellow of Trinity College and Cavendish Professor of Experimental Physics, Cambridge University_. (_Fourth printing._) _Price $1.50 net._ THE INTEGRATIVE ACTION OF THE NERVOUS SYSTEM. _By_ CHARLES S. SHERRINGTON, D.SC., M.D., HON. LL.D. TOR., F.R.S., _Holt Professor of Physiology, University of Liverpool_. (_Fifth Printing._) _Price $5.00 net._ RADIOACTIVE TRANSFORMATIONS. _By_ ERNEST RUTHERFORD, D.SC, LL.D., F.R.S., _Macdonald Professor of Physics, McGill University_. _Price $5.00 net._ EXPERIMENTAL AND THEORETICAL APPLICATIONS OF THERMODYNAMICS TO CHEMISTRY. _By_ DR. WALTER NERNST, _Professor and Director of the Institute of Physical Chemistry in the University of Berlin_. _Price $1.50 net._ PROBLEMS OF GENETICS. _By_ WILLIAM BATESON, M.A., F.R.S., _Director of the John Innes Horticultural Institution, Merton Park, Surrey, England_. (_Second printing._) _Price $5.00 net._ STELLAR MOTIONS. With Special Reference to Motions Determined by Means of the Spectrograph. _By_ WILLIAM WALLACE CAMPBELL, SO.D, LL.D., _Director of the Lick Observatory, University of California_.