Observations on Periodical Birds. 133 
A comparative view of ihe mean temperature of 
April and October, from 1817 to 1821 in- 
clusive. 
Years. 1%) 1818. 1819, | 1820. | 1821. Gen, 
means. 
April...) 46.8 | 45.1 | 50.5 | 50.7 | 48.5 | 48.3 
Oct. | 46,3;| 56.5] 50.1 | 47.7 | 50.5 | 50.2 
iy aes a a LD Ped 2A Aah) dla 
aig Pas +11.4|— 4 |—3.0 |+2.0 +1. 9 
A very near approximation is here obsery- 
able m the temperature of these months, 
allowing for the unusual warmth of the lat- 
ter in 1818: yet swallows and martins are 
almost the only summer birds seen in October, 
and they generally retire before the termina- 
tion of the second week ; though bats, field- 
inice, and various species of phalenz, tipule, 
musce, &c., are visible till the close of 
November; and even through the winter 
when the weather is open. In the year 1820, 
long-eared bats (vespertiliones auriti) were 
observed till nearly the middle of November: 
and in 1821, they were first noticed on the 
23rd of April, the mean temperature for the 
day being 50°.5, and were seen through 
November, to the 8th of December, when 
the mean temperature was 46°; the mean for 
November being 47°, which is within 1°.5 of 
that of April for the same year. 
