Page:Popular Science Monthly Volume 29.djvu/441

Rh rains. The object of exposing the bodies in this way is said to be to avoid polluting the earth by burying them. Throughout the Zoroastrian writings that remain, this principle is continually dwelt upon. Cremation is even a greater crime than interment of the dead, because, it was alleged, of the exceeding holiness and purity of fire, which must not be polluted. These views, it has been suggested, originated in the abhorrence of primitive Zoroastrianism for cannibalism and human sacrifices, on account of which it surrounded the dead human body with such awful horrors and observances as should effectually defend it against them.

The Flying Force of Birds.—Dr. Karl Müllenhoff has published, in the proceedings of the German Society for the Advancement of Aëronautics, a paper on the force exerted by birds in flying. The latest calculations, by Marey and others, give the maximum force exerted by birds at 1·2 to 1·4 kilogramme per square centimetre of muscular section—numbers that are not greater, but rather less, than those which represent the strength of other animals. Dr. Müllenhoff deduces from his own calculations that the labor performed by the wing in any time unit is little if any greater than that involved in walking on the ground. This result agrees with the facts shown by experiments that the weight of doves was not changed after considerable test-flights; and that it fell off only a few grammes after a flight of three or four hundred kilometres. Quite different from this are the results afforded by the experience, say, of velocipedists; one of whom confessed to the author that he had lost ten pounds after a few months of cycling, and who suffered after an hour or so of his exercise from a greatly quickened pulse and an intense heart-beating. Prechtl, of Vienna, some years ago published the conclusion that the force exerted by birds in changing their place was not greater than that of the other animals, and that the amount of force exerted by large and small birds was relatively the same. Helmholtz, twenty-seven years later, came to an opposite conclusion which he based, however, only on theoretical grounds. He predicated a geometrical similarity in the forms and movements of smaller and larger animals, and that a greater increase in power must be given the larger animals to overcome the greater resistance they have to encounter. Dr. Müllenhoff having subjected this theory to an experimental test, has found it not sound. The geometrical similarity of motions does not exist. While the wings of the larger birds move up and down, those of the smaller birds move diagonally, and of the smallest nearly horizontally. The author having also examined the rate of increase of velocity corresponding with increase of size, separately as regards vertical and horizontal movements, finds that increase in the weight of' the body is not accompanied by increase in the relative muscular mass; that the amount of absolute force does not increase as the bird becomes larger; that no differences are apparent between birds of different sizes in the velocities of the muscular contractions; and that, regarding differences in the quantity and quality of the food consumed by the larger and smaller birds—concerning which there is question—I while the labor performed in flight can be furnished only at the expense of a corresponding consumption of chemical elasticity, j we can so far not make any definite declaration concerning either the amount of substance consumed in flight-work, or the amount of food required to compensate for the substance that is consumed.

The Problem of the Irrawaddy.—Mr. Robert Gordon, who has recently addressed the Royal Geographical Society in support of his theory that the Irrawaddy is the outlet of the Sanpo of Thibet, says that that river presents the greatest geographical problem in Asia. Mr. Gordon's view is contradictory of the opinion generally held by geographers that the Sanpo is the Brahmapootra, a river that it must meet or run around before it can reach the Irrawaddy. In favor of his theory, he adduces the testimony of a number of Thibetan and Chinese authorities, dating from times of considerable antiquity; the size of the Irrawaddy in its upper course, which can not be supplied by the few small streams and the limited water-shed the geographers give it; the testimony of the names of various rivers and branches of rivers in