C 265 ] 
Received November 29, 1771. 
XX. An EJfay on the periodical Appearing 
and Dif appearing oj certain Birds , at 
different Times of the Tear . In a Letter 
from the Honourable Daines Barrington, 
Vice-Pref. R . S, to William Watfon, 
M. D. F. R. S. 
Dear Sir, 
*«£A P rii 2, 9, 30, it SI know, from fome converf- 
jn i ay 14, 1772. ation we have had on this head, 
that you confider the migration of birds as a very 
interefting point in natural hiftory, I fend you the 
following reflections on this fubjeCt as they have oc- 
curred to me upon looking into mod of the orni- 
thologifts who have written on this queftion. 
It will be firfi: neceflary in the prefent, as in all 
other difputes, to define the terms on which the 
controverfy arifes. I therefore premife that I mean 
by the word Migration, a periodical paflage by a 
whole fpecies of birds acrofs a confiderable extent of 
fea. 
I do not mean therefore to deny that a bird, or 
birds, may pofiibly fly now and then from Dover to 
Vol.LXIL Mm Calais^ 
