358 M IGRATION. 
each opinion have] udged mo ft proper for fupporting them.' 
We are lenfible of the great improbability of the third 
opinion, and know that many arguments have been ufed 
to prove its abfurdity : fuch as thefe ; The fwallow is 
lighter than water, and therefore cannot fink ; if it moults 
at all, it muft moult under water during its torpid Hate, 
which is very improbable ; there is no i'nftance of land- 
animals living fo long under water without refpiration. . 
Many other arguments of the fame fort have been ad¬ 
vanced, and certainly afford a fhort way of deciding the 
c]ueftion ; -but, unlefs they were fufficient to prove the 
immeriion of fwallows a •p'h'yfical impoflibility, they are 
of no force when oppofed to the evidence of teftimony, 
if there be no caufe to fufpefl the witnelfes of inaccuracy 
or defign. The true way to refute fuch an opinion is by 
accurate obfervation and experiment. We have not 
heard of any accurate inquiries being made by philofo- 
phers in thole northern countries where fwallows are faid 
to pafs the winter under water. Buffon, indeed, fhut up 
fome fwallows in an ice-houfe by way of experiment, 
which died in a few days ; but, as he does not tell us 
■what precautions he took to make the experiment fuc- 
ceed, it is not entitled to much attention. 
Mr. John Hunter made a very judicious experiment on 
the banks of the Thames, which is defcribed by a cor- 
refpondent in the Gentleman’s Magazine, who afferts 
that he had it from Mr. Hunter himfelf. One year in the 
month of September, he prepared a room, with every ac¬ 
commodation and convenience which he could contrive, 
to ferve as a dormitory for fwallows, if they were difpofed 
to deep in winter. He placed in the centre a large tub of 
water with twigs and reeds, &o. which reached to the 
bottom. In the corners of the room he contrived artifi¬ 
cial caverns and holes, into which they might retire 5 
and he laid on the floor, or fufpended in the air, different 
lengths of old wooden pipes, which had formerly been 
employed in conveying water through the ftreets, &c. 
When the receptacle was rendered as complete as poifible, 
be then engaged fome watermen to take by night a large 
quantity of the fwallows that hang upon the reeds in the 
Thames about the time of their departure. They brought 
bim, in a hamper, a confiderable number; and had fo 
nicely hit the time of their capture, that on the very day 
following there were’none to be feen. He put the fwal¬ 
lows into the room fo prepared, where they continued to 
fly about, and occafionally perch on the twigs, &c. But 
not one ever retired into the water, the caverns, holes, or 
wooden pipes, or fhowed the leaft difpofition to grow tor¬ 
pid, &c. In this fituation he let them remain till they all 
died but one. This, appearing to retain fome vigour, Was 
fet at liberty; when it mounted out of fight, and flew 
away. All the birds lay dead fcattered about the room ; 
but not one was found afleep or torpid, or had, if the cor- 
refpondent remembers, fo much as crept into any of the 
receptacles he had fo provided. Gent. Mag. May 1796. 
This experiment was ingenious, and certainly does 
render the doftrine of immeriion much more improba¬ 
ble ; but it is not deeifive ; for it may bill be urged by the 
advocates for that doflrine, as Mr. Kalm has done, that 
it may only bfe in the colder countries where fwallows re¬ 
tire into the water; and a letter of a more recent date, 
addreffed to Dr. Smith Barton, profeffor of natural hiftory 
in the univerfity of Philadelphia, goes very far indeed in 
proof of the fubmerfion as an irrefiftible law of nature. 
The letter is as follows : 
New York, July 18, 1800.—On the afternoon of the 
21ft of Auguft, 1798, as I was fitting in my parlour which 
looks towards the north, or Hudfon’s River, about fifty 
feet from the bank, in company with our mutual friend 
Mr. Jacob Sebor, our attention was attrafled by numer¬ 
ous flights of birds, which appeared to come acrofs the 
town from the eaftward, and defeend immediately into 
the river. So Singular an appearance excited our parti¬ 
cular obfervation. We went out and flood clofe to the 
bank, and then perceived that what we imagined at firft 
to be blackbirds, were actually fwallows ; and that, as 
fdon as the various ilocks had cleared the houles, and got 
direftly over the river, they plunged into the water, and 
difappeared. This was not confined to the vicinity of the 
place where we flood, burwas the cafe as far as the eye 
could reach, up and down the river, and continued with¬ 
out cefiation for nearly two hours, when the doling of 
the evening prevented our farther obfervation. Aware 
of the importance of affording any additional informa¬ 
tion on this Iong-dilputed qneflion in the natural hiftory 
of the'fwallow, I procured a telelcope, and watched at¬ 
tentively many of the flocks from their firft appearance 
until their immeriion, continuing my eye fixed upon the 
lpot long enough to be fully convinced that not one of 
the birds returned to the furface again. Indeed, one 
flock of about two hundred birds plunged into the water 
within thirty yards of us, and inftantly difappeared, with¬ 
out the leaft appearance of the oppolition that might be 
expected to arife from their natural buoyancy ; and at the 
fame time the evening was foferene, and the river fo un¬ 
ruffled, that no deception of our fight could poilibly have 
occurred. When the birds firft came in view, after croft¬ 
ing the town, their flight was eafy and natural; but, when 
they defeended near to the water, they appeared much 
agitated and diftreffed, flying in a confuted manner againft 
each other, as if the love of life, common ta all animals, 
impelled them to revolt againft this law of nature im- 
pofed upon their lpecies. As fome time has elapled fince 
the above-mentioned fafl occurred, I thought it proper, 
before I gave you Mr. Sebor’s name, as having been a 
witnefs to them, to confult his recolleftion on the fub- 
je£l; and I have pleafare in alluring you, he dillinftly re¬ 
members every circumltance I have recited, and of which 
I made a memorandum at the time. It may be worthy of 
remark, that, as far as any obfervation went, the fwallows 
totally difappeared on the 24th of Auguft, 1798 ; for, 
during the remainder of that year, I did not fee one. 
H. Pollock.” 
This curious fubjeff, however, ftill remains for the fur¬ 
ther inveftigation of philofophers and naturalifts ; and we 
{hall therefore infert the following note to the editor of 
the Monthly "Magazine for November 1802, which feems 
to account for the mode in which the writer of the above 
letter might have been deceived.—“ I know not whether 
the following obfervations concerning the common chim- 
ney-fyvallow, Hirundo ruftica, will be of fervice in proving 
any faffs relating to their migration ; but, not being an 
adept in .the fubjeft, and not being inclined to any parti¬ 
cular fyflem, I beg leave to offer them to the naturalill. 
On the 25th of September, I obferved the Hirundo ruf¬ 
tica begin to leave the town of N. and at one o’clock of 
the fame day there were but a few ftragglers left. But, 
happening to take a walk in the afternoon to the foutfi 
of the town, I obferved thoufands collected on the trees 
in Mr. M.’s park, bordering on a fifh-pondj There were 
a great many flying about, and efpecially over the water; 
and at every inllant numbers would dip under, and would 
even go fome way before they would come up; fo various 
were their evolutions, and lo rapid their motions, that 
it was very difficult to follow one that went in and out 
again. As foon as they had dipped, they retired to the 
neighbouring trees to dry themfelves; and a tree which 
was decayed, and had no leaves, was wholly covered. I 
am convinced, that one who pleaded for their retiring 
under water during the winter-l'eafon, might have been 
eaiily deceived ; but it appeared to me that they were 
cleanfing themfelves from the filth they had contracted, 
in order to lighten themfelves for their long and danger¬ 
ous journey. On the 26th they all went away ; and the 
water, which the evening before was a feene of confufion, 
was now lilent.” 
Such is the evidence we have been able to collefl; and 
our readers will probably agree with us, that neither of 
the three opinions is fupported by fuch evidence as to 
fatisfy the mind completely. Opinions reipeoting events 
1 wlych 
