4 ON THE MIGRATION OF BIRDS. 
1st. The Summer Birds, or those species which ap- 
pear during the spring months and retire in autumn. 
Ynd. The Winter Birds, or those species which ap- 
pear during the autumnal months and withdraw in 
spring. 
8rd. Birds which are irregular in the times of their 
appearance and disappearance. 
4th. Birds which are partially periodical, retirmg in 
particular districts only. 
The Tables contain those species of Periodical Birds 
which visit the neighbourhood of Manchester, classed 
according to the above method; the times of their 
arrival and departure, taken at an average of fifteen 
years’ observations, commencing with 1814 and ter- 
minating with 1828, and the general mean tempera- 
ture of those days on which they have appeared and 
disappeared during that period, found from the ex- 
tremes indicated by a pair of Rutherford’s horizontal 
self-registering thermometers exposed to the open air 
in a shady situation, being also given. 
It is proper to intimate that I have employed the 
nomenclature of the second edition of M. Temminck’s 
‘Manuel d’Ornithologie’ throughout the volume in 
treating upon European birds; but that, as regards 
extra-European species, the names, for the most part, 
are accompanied by the authorities I have adopted. 
