EVOLUTION OF THE STELLAR SYSTEMS. 225 
available in the books at my disposal (Humboldt’s Cosmos, Herschel’s Outlines, ete.), I 
discovered to my surprise that unlike the orbits of the planets and satellites, they are 
very eccentric, though not so eccentric as those of the periodic comets. It was at once 
evident that it would be hopeless to attempt to explain the origin of the stellar systems, 
if we could not explain the cause of the high eccentricities of the orbits. The next day 
I called on Prof. Smith and told him of the discovery that the orbits are very eccentric, 
and asked whether he thought [ might explain this peculiarity on the tidal theory ; rub- 
bing his head for a moment in quiet reflection, he replied: “Oh! I see what you mean ; 
you think the dragging of the tides in the bodies of the stars has produced the elongation 
you find in the orbits. Such an idea can hardly be discussed off-hand, but it is at least 
worth examining; it may prove fruitful.’ “That is exactly what I mean,” said I, 
“and you have correctly interpreted my line of thought.” After this conversation, which 
is here reported exactly as it occurred,* there was nothing else before my mind for 
several days, as I was wholly occupied with finding out whether the problem undertaken 
was soluble, and, if so, whether it would result in any important Physical Truth. Having 
established the fact of high eccentricity as thoroughly as the published orbiis at my dis- 
posal would admit, I set about that same day the problem of explaining the cause of 
the eccentricities ; and as I worked the impression continued to grow on the mind that 
since the stars are not solid, but self-luminous fluid bodies like our sun, and the two 
members of a system comparable in mass, the action of each body would produce tides in 
the other, and the lagging of-the tides in the two stars would gradually expand and 
elongate the orbits as now observed in space. And before I had obtained access to the 
learned papers which Darwin had communicated to the Royal Society, or even to his 
5) 
article ‘‘ Tides” in the Hneyclopedia Britannica, I proved by an elementary process that 
when the bodies rotate more rapidly than they revolve, the eccentricity of the orbit would 
gradually increase. Here then was a result confirmatory of the happy intuition, and 
for the past nine years my energies have been largely devoted to the extension and 
generalization of the theory of bodily tides in relation to cosmical evolution. 
After concluding my undergraduate studies at the University of Missouri, I con- 
tinued the work at the University of Berlin. It is particularly of that work and the 
extension which I have since made of it that I shall speak to-night. The theory of tidal 
friction developed in the Inaugural Dissertation presented to the Faculty of the Uni- 
yersity of Berlin is essentially a special treatment of the general theory as it occurs in 
nature, while that previously developed by Darwin in connection with the moon and 
planets is restricted by the condition that the perturbing body is very small. I shall 
therefore discuss the general case as presented in my own researches. 
_ *As the occasion of my beginning this work has never been published, I trust it will not be thought inappropriate 
for me to recall it in this paper to the American Philosophical Society. 
