SCIENCE SIFTINGS

New Zealand Tablet, 26 May 1921, Page 46

SCIENCE SIFTINGS

(By “Volt.”)

The skill shown by bats in avoiding objects during their flight is familiar. Says a writer in the Lancet (London, October 2): “Three views have been propounded to explain this phenomenon—(l) That bats are endowed with very keen sight, which enables them to see when everything is dark to man. (2) That their sense of touch is extraordinarily acute, particularly at the wing-tips. (3) That they possess some sense the knowledge of which is not possessed by men. In a recent number of the Journal of Physiology Dr. Hamilton Hartridge criticises and discards all three views, in view of his own experiments. On summer evenings pipistrel —sometimes between one and two hundred at a time used to fly through the open windows into the adjacent rooms communicating by an intervening door, capable of being illuminated by electric light or completely darkened. As a rule, in the rooms the bats all flew roughly in the same direction, but even when the electric light was turned off nothing indicated that collisions occurred. Even when threads were placed in their path it appears that bats in full flight and in what seems to be absolute darkness can not only steer round a room and avoid one another, but can avoid obstacles such as threads. Further, that they can tell whether a door is shut or open wide, or just sufficiently wide open to allow them to pass. The hypothesis is advanced that the flight of bats is directed, by a special sense of hearing, since the soundwaves of short wave-length which they are known to emit are capable of casting shadows and of becoming soundpictures.” Why the Sky is Blue. After astronomers and scientists had puzzled over this apparently simple question for many hundreds of years, Professor John Tyndall, a famous scholar of the last century, solved the mystery with the following explanation: Sunlight is pure white light, made up of rays of the seven primary colors seen in the rainbow— ■ orange, yellow, green, blue, indigo, and violet. The sky, which is really the air surrounding the earth, is filled with myriads of tiny specks or particles of matter which absorb some of the colors in the rays of sunlight and reflect others—forming the combination we call sky-blue. The variations in shade of this blue are due to the fact that the atmosphere is, at different times, filled with varying densities of these dust-particles, and also to the varying angles at which the sunlight strikes them. After rain the air is washed comparatively clear, and the sky then appears as the true blue we are accustomed to associate with it. r lf one could penetrate beyond the shell of air surrounding the earth, the sky, instead of being blue, would appear to be pure white, because there would be nothing to impede the direct rays of the white sunlight. A Long-Lived Animal. A tortoise is usually defined as a terrestrial turtle, one that lives on land, although “tortoise-shell” is fixed as the name of the commercial product of certain sea-turtles. The tortoise is a slow-moving and slow-living animal, but its life is as long as its movements are deliberate. Specimens of small species have been known to live more than a hundred years and one, at least, more than a hundred and fifty years (says Ave Maria). There was in existence in Mauritius a few years —and, for what we know, nfay be in existence still—a large tortoise whose Recorded history goes back to 1766. The largest collection of all living species of tortoises is that at Tring Park, England, where the biggest known tortoise is one measuring 56 by 49 inches over the curve of its shell. It was taken from Duncan Island in 1813, and is still, perhaps, in good condition at the age of more than a century. L -