OBITUARY NOTICES. 
449 
cess of the student of terrestrial physics depends upon the 
acumen with which he distinguishes between the important 
and unimportant forces that underlie a given phenomenon. 
After separating the essential factors from the less impor¬ 
tant, the treatment of the subject has to be pursued accord¬ 
ing to ordinary deductive methods, abundant illustrations 
of which are found in astronomical and molecular physics. 
In this latter process Ferrel was equally skillful, thorough, 
and patient. At the risk of lengthening my remarks to a 
rather greater extent than is ordinarily expected in the 
short biographical notices of our Society, I will take the 
liberty of enumerating a number of special cases wherein, 
I think, Ferrel showed his ability and advanced beyond 
other investigators. 
If we take up these points chronologically we might 
almost begin with his boyish attempts to predict the eclipses 
of the sun and moon, when, without ever having seen an 
astronomy and having only the predicted places of the sun 
and moon as given in the farmers’ almanacs for several suc¬ 
cessive years, he figured out the recession of the moon’s 
node on the ecliptic, the irregularity of the moon’s motion 
in its orbit, and the inclination of the orbit to the ecliptic, 
proceeding thus until finally he was able to predict the oc¬ 
currence of the solar and lunar eclipses to within a few 
minutes of time. 
(1.) Ferrel’s first scientific paper, published in 1853, when 
he was thirty-five years of age, was based wholly upon his 
own studies of Newton’s “Principia” and Laplace’s “Mecan- 
ique Celeste,” and it does not appear that up to that time he 
had ever had any personal intercourse with mathematical 
investigators of like tastes with himself. It is therefore all 
the more surprising that in this memoir he boldly develops 
a conclusion that he had conceived several years before, 
namely, that the sun and moon must have an effect upon 
the rotatory motion of the earth by reason of the friction be¬ 
tween the tidal wave and the earth, whereby the length of 
the day is slowly increasing from age to age. He further- 
59—Bull. Phil. Soe., Wash.. Vol. 12. 
