Science Sittings

New Zealand Tablet, 10 December 1908, Page 35

Science Sittings

by • volt

The Life of Trees. Trees, like animals, eat, sleep, grow and die. Every one knows this, yet not every one is aware that trees tear their, clothes and have to mend them ; that they jostle one another like rude boys in a crowd, the strong overpowering the weak. Disease besets them. Accidents break their limbs. The varying weather cheeks their growth or coaxes them to flourish. Kin of the bear, they put "on warm coats in winter- and wait for spring. When the weather is warm a tree goes to sleep at sundown and in the morning wakes again. A cloudy sky makes the tree drowsy. Rain puts it to sleep. So the only days of prosperity and tree activity are the clear days. In sleep the leaves of many trees fold together and droop. The closing of the leaves checks the cooling process of evaporation s and maintains bodily heat. All young and tender foliage tends thus to curl up to sleep when the weather is bad or night is in the sky. Older and stiffer Reaves go to sleep sitting up, just 1 like grandfather in his arm chair. The breathing of the tree is as necessary as is the breathing of animals. All life consists of a continuous building up and tearing down of cells. The material for building new cells is made of food taken in and elaborated — made over — by intricate chemical processes. The oxygen in the air is one of the chemical ingredients both in destroying and building the cells of animals and trees. The leaves are the lungs, which inhale carbon dioxide and exhale pure oxygen. The Forth Bridge. The Forth bridge is a wonderful structure. It is a mile and a half long, and is the highest bridge in the world, being 450 feet from the base to highest point. The cantilever principle was adopted in its construction. Each cantilever consists of two brackets, the lower (in ordinary position) supporting the railway by compression, and the upper (inverted) by tension — the two being firmly interlaced and practically indestructible. The masonry piers upon which the cantilevers rest are founded at from 50 to 90 feet under water level, and vary in diameter from 70 feet at the bottom to 60 feet at tlie top. The depth of the water in the centre of the channel is 210 feet. ' The main piers of the cantilevers are of steel tubes, 12 feet in diameter, - carried up to a height of 370 feet, whilst the rails are 160 feet above high-water level. The two main spans are each 1710 feet, with a span on either side between the cantilevers and the viaduct piers of 675 feet. The entire superstructure is of steel, 42,000 tons of which were used, while 12,000 tons of iron were used, in the foundation, including 32 miles of bent plate for the tubes, the whole being welded together by eight million rivets. ' As the bridge has a ''metal surface of 120 acres, it took no less than 250 tons of paint and 35,000 gallons of oil to paint the work.

■ - The Clothes Moth. One of the most widely celebrated and anciently detested of insect pests is the clothes moth (writes- Sir Bay Lankester in the Daily Telegraph). It is the caterpillar of. this moth -which is objectionable — biting off, eating, and using as a case the hair of furs and the fine filaments of woollen fabrics. Not everyone is able to recognise the clothes moth, which is a very small creature of a greyishyellow color. The wings when set for flying measure only half an inch in expanse, and when the moth is walking or at rest, shut closely to the body so as to give it^an almost cylindrical shape, with an attenuated snout. Much bigger moths occasionally get into our rooms, but, do no harm. These little clothes moths lay their eggs on fur or wool, and the caterpillars which hatch from them do' the damage. The moths themselves have no jaws and take, no food. But the caterpillar or grub, though soft and readily crushed, has a pair \of very hard, minute dark-colored jj a wsy with which it works away, cropping the fur and wool on. which it lives. The moths i are seen in houses commonly between January and October, and it is, of course, the object of the. victimised householder to destroy them before they can lay eggs, or, what is more practical, to keep woollen and fur clothes away from their reach.