LIFE OF WILSON. cciii 
recorded their testimony, in the most positive manner, against tor- 
pidity. 
The Memoir on the Migration and Torpidity of Swallows,” 
wherein Dr. Barton was confident he should be able to convince 
every candid philosopher of the truth of his hypothesis concerning 
these birds, never issued from the press, although so publickly an- 
nounced. And who will venture to say that he did not, by this 
suppression, manifest his discretion ? AVhen Wilson’s volume, 
wherein the Swallows are given, appeared, it is probable that the 
author of the “ Fragments” was made sensible that he had been 
writing upon subjects of which he had little personal knowledge; 
and therefore he wisely relinquished the task of instructing philoso- 
phers, in these matters, to those more capable than himself of such 
discussions. 
Naturalists have not been sufficiently precise when they have 
had occasion to speak of torpidity. They have employed the term 
to express that torpor or numbness, which is induced by a sudden 
change from heat to cold, such as is annually experienced in our 
climate in the month of March, and which frequently affects S\val- 
lows to so great a degree as to render them incapable of flight. 
From the number of instances on record of these birds having 
been found in this state, the presumption has been that they wei e 
capable of passing into a state of torpidity, similar to that of the 
Marmots, and other hybernating animals. 
Smellie, though an advocate for migration, yet admits that 
Swallows may become torpid. “That Swallows/’ says he, “in 
the winter months, have sometimes, though very rarely, been found 
in a torpid state, is unquestionably true. Mr. Collinson gives the 
evidence of three gentlemen who were eye-witnesses to a number 
of Sand-Martins being drawn out of a cliff on the Rhine, in the 
month of March, 1762.”* One should suppose that Smellie was 
* Philosophy of Natural History, chap. 20. 
