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Untitled Article
muscles , and through the bones of birds ? They can , in reality , add little to the levity of the body , and must be subservient to some more important purpose in their economy . It certainl y must be admitted that , notwithstanding the researches of Nitszch and Tiedemann , the subject is involved in much obscurity . One use , however , of this remarkable provision is very manifest , inasmuch
as it obviously enables the bird to transport itself with impunity from the lower into the higher regions of the atmosphere . It is well known that the animal heat bears an increasing proportion with the rapidity of the circulation and respiration , so that the animal heat of birds is hi g her than that of mammalia . The air , therefore , diffused through their body must be in a rarefied state , and hereby the bird is enabled to ascend into the upper strata of
the air without experiencing any inconvenience from the sudden change of atmospheric pressure . If we climb the Andes , or ascend a few hundred feet above the level of the sea , we experience very considerable uneasiness , because the air within the body being denser than the air without , exerts a pressure from within which externall y meets with no counterpoise . Were the change effected
gradually , we mi g ht accustom ourselves to live in a much more rarefied atmosphere than that b y which we are now surrounded , because the air within the bod y would by degrees become of the same density as that without , and , consequently , no such pressure would be exerted . Accordingly , the air which pervades the bod y of a bird of flight , being rarefied , corresponds with the rarefied state of the air in those higher regions into which it soars :
o *^ * besides which , it is by no means improbable that birds have a command over the quantity of air which enters these air-cells , just as fish have over the air which is contained in their swimming bladder . It must , however , be confessed , that no experiments ot any consequence have been made on this curious subject since the days of Camper and Hunter ; and we , therefore , rejoice to observe
that investigations have been recently made upon it b yM . Jacquernin , who has just submitted his experiments and inferences to the consideration of the Academic Koyale des Seiences , the report of which we anticipate with interest . We have ventured to make these observations without any wish whatever to disparage the views of Mr . Mudie : his volume is replete with facts in the highest decree interesting to the naturalist ; and when wo meet him on the
debatable ground of theory , we do so in the spirit of good fellowship , fully assured that he will appreciate any suggestion which appears justified by evidence * , for he has walked as an acute observer through the fields , and forests , and among the mountain * , and we all know that " Nature never did betray the heart which loved her . "
Untitled Article
The Study of Birds . 275
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Citation
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Monthly Repository (1806-1838) and Unitarian Chronicle (1832-1833), April 2, 1835, page 275, in the Nineteenth-Century Serials Edition (2008; 2018) ncse.ac.uk/periodicals/mruc/issues/vm2-ncseproduct2644/page/51/
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