that they feldom fing any thing but fhort and loud jerks, which confequently cannot be compared to the note of a caged bird, as the inftrument is overstrained.

I muft alfo here observe, that my nightingale was a very capital bird; for fome of them are so vastly inferior, that the bird-fanciers will not keep them, branding them with the name of Frenchmen.

But it is not only in tone and variety that the nightingale excels; the bird alfo fings (if I may fo exprefs myself) with fuperior judgment and taste.

I have therefore commonly obferved, that my nightingale began foftly, like the ancient orators; referving its breath to fwell certain notes, which by this means had a moft aftonishing effect, and which eludes all verbal defcription.

I have indeed taken down certain paffages which may be reduced to our mufical intervals; but though by thefe means one may form an idea of fome of the notes ufed, yet it is impoffible to give their comparative durations in point of mufical tune, upon which the whole effect muft depend.

I once procured a very capital player on the flute to execute the notes which Kircher hath engraved in his Mufurgia, as being used by

the nightingale; when, from want of not being able to fettle their comparative duration, it was impoffible to obferve any traces almost of the nightingale's fong.

It may not be improper here to confider, whether the nightingale may not have a very formidable competitor in the American mocking-bird +; though almost all travellers agree, that the concert in the European woods is fuperior to that of the other parts of the globe.

As birds are now annually imported in great numbers from Afia, Africa, and America, I have frequently attended to their notes, both fingly and in concert, (which certainly are not to be compared to thofe of Europe.

Thomson, the peet, (whofe obfervations in natural history are much to be depended upon) makes this fuperiority in the Europeanbirds to be a fort of compensation for their great inferiority in point of gaudy plumage. Our goldfinch however, joins to a very brilliant and pleafing fong, a most beautiful variety of colours in its feathers.

It must be admitted, that foreign birds, when brought to Europe, are often heard to a great difadvantage; as many of them, from their great tamenefs, have certain

ly

ly been brought up by hand, the confequence of which I have already ftated from feveral experiments. The foft-billed birds alfo cannot be well brought over, as the fuccedaneum for infects (their comnon food) is fresh meat, and particularly the hearts of animals.

I have happened, however, to hear the American mocking-bird in great perfection at Meff. Vogle's and Scott's, in Love-lane, Eastcheap.

This bird is believed to be ftill living, and hath been in England thefe fix years. During the space of a minute, he imitated the woodlark, chaffinch, blackbird, thrush, and fparrow. I was told alfo, that he would bark like a dog; fo that the bird feems to have no choice in his imitations, though his pipe comes nearest to our nightingale of any bird 1 have yet met with.

With regard to the original notes, however, of this bird, we are fill at a lofs; as this can only be known by those who are accurately acquainted with the fong of the other American birds.

Kalm indeed informs us, that the natural fong is excellent; but this traveller feems not to have heen long enough in America to have diftinguished what were the genuine notes: with us, mimics do not often fucceed but in imitations.

I have little doubt, however, but that this bird would be fully equal to the fong of the nightingale in its whole compais; but then, from the attention which the mocker pays to any other fort of difagree able noifes, thefe capital notes would be always debafed by a bad

mixture.

We have one mocking bird in England, which is the skylark; as, contrary to a general obfervation I have before made, this bird will catch the note of any other which hangs near it; even after the skylark note is fixed. For this reafon the bird-fanciers often place the skylark next one which hath not been long caught, in order, as they term it, to keep the caged skylark honeft.

The question, indeed, may be afked, why the wild fkylark, with thefe powers of imitation, ever adheres to the parental note; but it must be recollected, that a bird, when at liberty, is for ever fhifting its place, and, confequently, does not hear the fame notes eternally repeated, as when it hangs in a cage near another. In a wild ftate, therefore, the fkylark adheres to the parental notes; as the parent cock attends the young ones, and is heard by them for fo confiderable a time.

I am aware alfo, that it may be afked, how birds originally came by the notes which are peculiar to each fpecies. My answer, however, to this is, that the origin of the notes of birds, together with its gradual progrefs, is as difficult to be traced, as that of the different languages in nations.

The lofs of the parent-cock, at the critical time for inftruction, hath undoubtedly produced thofe rarities, which I have before obferved are in the fong of each fpecies; because then the neftling hath either attended to the fong of fome other birds; or, perhaps, invented fome new notes of its own, which are afterwards perpetuated from generation to generation, till fimilar

accidents produce other alterations. The organs of fome birds alfo are probably fo defective, that they cannot imitate properly the parental note, as fome men can never articulate as they should do. Such defects in the parent- bird muft again occafion varieties, because these defects will be continued to their defcendants, who (as I before have proved) will only attend to the parental fong. Some of thefe defcendants alfo may have imperfect organs; which will again multiply varieties in the fong.

The truth is, as I before obferved, that scarcely any two birds of the fame fpecies have exactly the fame notes, if they are accurately attended to, though there is a general resemblance.

Thus most people fee no difference between one fheep and another, when a large flock is before them. The fhepherd, however, knows each of them, and can fwear to them if they are lot; as can the Lincoln fhire gofherd to each goofe.

On the noxious Quality of the Effluvia of putrid Marshes. In a Letter from the Rev. Dr. Priestley to Sir John Pringle.

[Read, Dec. 16, 1773.] INCE the publication of my papers, I have read two treatifes, written by Dr. Alexander of Edingburg, and am exceedingly pleafed with the fpirit of philofophical inquiry which they difcover. They appear to me to contain many new, curious, and valuable obfervations but one of the conclufions, which he draws from his experiments, I am fatisfied, from

my own obfervations, is ill founded, and, from the nature of it, must be dangerous. I mean his maintaining, that there is nothing to be apprehended from the neighbourhood of putrid marshes.

I was particularly furprized to meet with fuch an opinion as this in a book infcribed to yourself, who have fo clearly explained the great mifchief of fuch a fituation in your excellent treatife on the difeales of the army. On this account, I have thought it not improper to addrefs to you the follow. ing obfervations aad experiments, which I think clearly demonstrate the fallacy of Dr. Alexander's reafoning, indifputably establish your doctrine, and, indeed, juftify the apprehenfions of all mankind in this cafe.

I think it probable enough, that putrid matter, as Dr. Alexander has endeavoured to prove, will preferve other fubftances from putrefaction; because, being already faturated with the putrid effluvium, they cannot readily take any more; but Dr. Alexander was not aware, that air, thus loaded with purid effluvium, is exceedingly noxious when taken into the lungs. I I have lately, however, had an opportunity of fully afcertaining how very noxious fuch air is.

Happening to ufe, at Calne, a much larger trough of water, for the purpose of my experiment, than I had done at Leeds, and not having fresh water fo near at hand as I had there, I neglected to change it, till it turned black, and became offenfive, but by no means to fuch a degree, as to deter me from making ufe of it. In this ftate of the water, I obferved bubbles of air to rife from it, and especially in one

place,