Science Siftings

New Zealand Tablet, 25 April 1912, Page 59

Science Siftings

, , By * Volt.- O v The Necessity of Ballast. ' Have you ever wondered (says a writer) why it is that a bird flies so surely and straight where he wants t(J go, while a butterfly flits about in such a haphazard way? Those of you who had had to do with boats will know what ballast is, and how necessary it is to a boat’s even, steady progress. The weight of the boat should be well down in the water. The bird is like a well-ballasted boat. The heavy muscles and the stomach, with its weight of food, are all in the ‘hold,’ so to speak — all down as low as possible —and the expanse of the wing is not great enough to outbalance this. In the case of the butterfly the wing expanse is so great and the weight of the body so little that the insect flutters about, driven out of its course by every breath of air. * • Telegraph Lines in Tropical Countries, j In tropical countries the maintenance of a telegraph line in good order is a constant uphill fight against all manner of interrupting enemies that operators and linemen in this country never dream of. In tropical South America the wires get tangled up with the cable-like web of an immense spider, which, dripping with dew or rain, makes cross connections, ‘short circuits,’ and * grounds ’ almost' daily. Ants often destroy the poles in a few weeks. In the West India Islands the turkey buzzards make life miserable for the telegraph and telephone people. These big, heavy birds —the only scavengers— abound in great numbers. They roost on the wires or fly against them, and invariably break them off short. In one large town the telephone lines that ran by the public market had to be put underground because the buzzards congregated there in great numbers, rested on the wires, and broke them almost nightly. On the pampas of Argentina the herds of practically wild cattle rub and butt against the poles, and frequently break them down. The Study of Air Currents. Until men began to navigate the air and study its currents and movements little attention was paid to the conditions of the upper atmosphere, and such matters as atmospheric tides and top currents , completely encircling the earth were of seemingly little interest. Since men have flown, and especially since men have flown and fallen, we have heard a great deal in a vague way of air currents. Recently Mr. Lawrence Hodges in a paper before an English scientific body gave some unique facts about air tides which are not generally known. The moon, we know, causes the marine tides by its attraction. It draws the water on the surface of the earth toward it in a hump on the side that is exposed to the lunar influence, and draws the earth itself away from the water on the opposite side, leaving a corresponding hump of water. The air, it seems, is affected in the same way. The layer of atmosphere about the earth rises, falls and' flows more freely than water, because it is lighter, so. the tide comes more quickly in the air at a given spot than the marine tide. This rise and fall, however, means just as much to the navigator of the air as the tide in the sea does to the sailor, and has to be accounted for. The most remarkable current, however, is one constant stream in the atmosphere running from west to east completely around the earth in the upper atmosphere. This was first brought to public attention- when the volcano Krakatao blew a cubic mile of matter into the upper atmosphere in the ’Bo’s. The lighter particles to make a complete circuit of the earth seven times in this circumglobular current before they finally disappeared.