ELISHA MITCHELL SCIENTIFIC SOCIETY 33 
so long as the true value is set upon it and fancy is not allow- 
.ed to obscure fact nor to be mistaken for it. "The hypothesis 
proposed is simple and if true will be very helpful. It will be 
a great step forward if it can be shown that the doctrine of 
valence is a doctrine of vibratory equilibrium. 
PRELIMINARY CATALOGUE OF THE BIRDS OF 
CHAPEL HILL, N. C., WITH BRIEF NOTES 
ON SOME OF THE SPECIES. 
T. GILBERT PEARSON. 
INTRODUCTION. 
In this catalogue are enumerated the species of birds, 
known to have been observed and positively identified at 
Chapel Hill. While the list is incomplete, and is presented 
only as a preliminary catalogue, the author expresses the 
hope that it may prove of use to those interested in the orni- 
thology of the region, and that it may serve asa basis for 
more extended observations. In addition to the enumeration 
of the species, the paper contains some brief notes on the mi- 
gration and nesting habits of such forms as have come under 
the writer’s observation at Chapel Hill. 
The difficulty of preparing a complete catalogue of the 
birds may be readily understood when we recall the fact that 
the bird population is constantly changing, The great wave 
of the autumnal migration carrying large numbers of north- 
ern birds past us, at the same time taking many of our sum- 
mer forms, scarcely subsides, before the swell sets back from 
the south, sweeping hosts of birds of passage to us on their 
northern journey. Some migrants found to be numerous 
during the fall migration may be extremely rare in the spring, 
and wice versa. Birds which nosmally do not occur in a 
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