DAILY MIRACLES

Evening Star, Issue 19290, 1 July 1926, Page 12

DAILY MIRACLES

The application of heat to any hotly causes expansion and affects the density of it. The size of a fixed weight of a substance varies according to the heat applied, and so the weight of a piece of copper of fixed size will vary considerably according to the temperature at which it is weighed. A liquid or solid that is of less weight in relation to a portion of another liquid of the same size, providing they do not mix, will float on_ top of the heavier liquid. Thus, a ship or similar hollow vessel made of metal or other heavy material will float in water because the interior is filled with air, a very light substance; and the average weight of the substances which fill the space taken up by the ship' or vessel is less than that of the quantity of water necessary to fill an equivalent space. For the opposite reason, a solid piece of moral or stone will sink. CONVECTION CURRENTS. 'This principle is of particular interest when a largo quantity of a liquid or gas in an open container is heated in only ono spot. The heated pari expands more than the rest, becomes lighter in proportion, and floats to tho top. The colder part flows down to take its place, eventually gets hotter still, and itself rises; while the part first Related thou flows to the bottom again. This process is repeated, and sets up a continuous current flowing to the top from tho heated spot, and then down tho sides and inwards towards that spot. In this way ocean currents and winds arise. The earth being hottest at the Equator, the air there is always rising, and air from the cooler parts 9! tho earth rushes in from the direction of the Polos to take its place. ■ But for the revolution of the earth through space at high speed there would bo winds blowing from due north and south towards the Equator. However, a point on the Equator moves much faster relatively than a point near the Poles, and this causes the winds to blow slightly N.E. and S.E. These winds, known as the trade winds, are strongest and only really noticeable in the tropics. DOMESTIC APPLICATIONS. The Gulf Stream is due to similar causes, and draughts in a room are due to tho cold air coming in from the outside to take the place of hot' air that has risen up the chimney. This principle is applied to domestic hot-water systems. The boiler is usually situated in the lower part of the house, with the cistern at the top, connected to it by two pipes, one of which leads to the ton and the other to the bottom of the boiler. The hot water risefc to the top of the boiler through the pipe to the cistern, and the cold water flows from tho cistern through the other pipe to tho bottom of the boiler, giving a continuous circulation of the water through tho boiler. In this way the water gets hotter and hotter much more quickly than if there were no such currents.—‘John o’ London’s' Weekly/ j