Il regno di diritto . nceasing evoluzioni sembrano parte di happinessof estate e di serena e lofty skies.* Ci sono altri uccelli in cui l'ala ha tobe atta al duplice scopo di nuoto,o piuttosto di immersioni subacquee e di volo. In questo caso, dsupporto grande area di anta deve essere erogato con, essere-cause sarebbe incapace di essere lavorato sott'acqua. Di conseguenza in tutte le immersioni uccelli il wingsare ridotto per le dimensioni più piccole che isconsistent con ritegno del potere di volo a tutti i;e in un paio di forme estreme, il potere di volo issacrificed complessivamente, e l'ala è ridotto finoal s

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The reign of law . nceasing evolutions seem part of the happinessof summer and of serene and lofty skies.* There are other birds in which the wing has tobe adapted to the double purpose of swimming, or rather of diving, and of flight. In this case, alarge area of wing must be dispensed with, be-cause it would be incapable of being worked underwater. Consequently in all diving birds the wingsare reduced to the smallest possible size which isconsistent with retaining the power of flight at all;and in a few extreme Forms, the power of flight issacrificed altogether, and the wing is reduced tothe size, and adapted to the function, of a powerfulfin. This is the condition of the Penguins; Butin most genera of swimming Birds, both purposesare combined, and the wing is just so far reducedin size and stiffened in texture as to make it work-able as a fin under water, whilst it is still just large * For the form of the wing in this remarkable bird, see the beauti-ful drawing here engraved from the pencil of Mr Wolt. CONTRIVANCE A NECESSITY. 155 enough to sustain the weight of the bird in flight.And here again we have a wonderful example ofthe skill with which inexorable mechanical lawsare subordinated to special purpose. It is a neces-sary consequence of the area of the wing being soreduced, in proportion to the size of the bird, thatgreat muscular power must be used in working it, otherwise the Force of Gravity could not be over-come at all. It is a farther consequence of thisproportion of weight to working power, that theremust be great momentum and therefore great velo-city of .flight. Accordingly this is the fact with allthe oceanic diving Birds. They have vast distancesto go, following shoals of fish, and moving fromtheir summer to their winter haunts. They all flywith immense velocity, and the wingrstrokes areextremely rapid. But there is one quality whichtheir flight does not possess—because it is incom-patible with their structure, and because it is notrequired by thei

Parole chiave associate all'immagine

• bookauthor
• bookcentury1800
• bookdecade1860
• booksubjectcosmology