82 HISTORY OF 



Thus there are some birds which, by migrating, make an ha- 

 bitation of every part of the earth ; but in general every climate 

 has birds peculiar to itself. The feathered inhabitants of the 

 temperate zone are but little remarkable for the beauty of their 



lethargic state, to enjoy the benefits of the season. And what in some mea- 

 sure seems to give stability to this supposition is, that the animals in ques- 

 tion take up their abodes a little below the surface of the soil ; some in the 

 crevices of walls, or interstices of rocks j and others, such as frogs, female 

 coads, and water-ne%vts, bury themselves in the mud of shallow ponds. In 

 the former of these retreats they are only covered by a thin layer of earth ; 

 and in the latter, by the addition of a shallow sheet of water ; consequently 

 they are re-animated in due season, by the genial rays of the sun, after he 

 has entered the northern half of the ecliptic. Dr Hales has proved by ex- 

 perimental facts, that the bulb of a'thermometer buried 16 inches below the 

 earth's surface, stood at 25° of his scale in September, at 16° in October, and 

 at 10" in November, during a severe frost ; from which point it ascended 

 again slowly, and reached 23° in the beginning of April, (old style.) Now 

 the end of September, and beginning of October, is the season the hedgehog, 

 shrew, bat, toad, and frog disappear : and about the middle of April these 

 animals re-appear ; which agrees very well v^ith the variations of tempera- 

 ture of the preceding theory. 



The migratory birds of this country are very numerous ; how comes it 

 then that they are never found near the surface of the earth, as is the bat, 

 hedgehog, &c. ? A few solitary facts of birds being found in holes, in old 

 walls, and in the earth, are on record ; but this is by no means a sufficient 

 reason for establishing a theory of their remaining in a state of torpidity 

 diuung the winter. 



The temperature of places situated at great depths below the surface of 

 the laud and water, is sufficient objection to the circumstance of birds re- 

 maining in a torpid state, during the winter, in solitary caverns, or at the 

 bottom of deep lakes. It is a known fact, that all places situated 80 feet 

 below the surface of the earth, are constantly of the same temperature. Mr 

 Boyle kept a thermometer for a year imder a roof of 80 feet in thickness, 

 and found that the liquor in the instrument remained stationary all the 

 time. Dr Withering made a similar experiment on a well 84 feet deep, and 

 found it remained at 49° for the year round. Siu-ely this invariable tem. 

 perature is inconsistent with the theory of birds remaining in a state of tor. 

 pidity in deep lakes, or solitary caverns, where the sun has no influence ; 

 for what would call forth their dormant organs into action ? the vernal sun 

 having no influence on places so situated. It is but reasonable to conclude, 

 that cold which kept them benumbed by its sleepy torpor, would evidently 

 perpetuate their slumbers. 



This state of torpor is obviously analogous to sleep ; but it differs from 

 sleep in being occasioned solely by temperature. — Hybermatiug animalB 

 always assume this torpid state, whenever the thermometer sinks to a cer- 

 tain i)oint. Almost all animals seem to be susceptible of tliis state, at least 

 to a certain extent, not even excepting man. For the apparent death pro. 

 duced by cold is probably nothing else but a species of torpor, out of wliich 

 the animal, in most cases, might be roused, if the requisite caution in ap. 



