DAILY MIRACLES

Shannon News, 9 July 1926, Page 4

DAILY MIRACLES

The application of heat to any body causes expansion and affects the density of it. The size of a fixed weight of a substance varies accord, ing 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 weighted. A liquid or solid that is of less weight in relation to a portion of another liquid of th e 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 th e opposite reason, a solid piece of hietal or stone will sink. Convection Currents. This principle is of particular interest when a large quantity of a liquid or gas in an open container is heated in only one spot. The heated part expands more than the rest, becomes lighter in proportion, and : floats to the top. The colder part ; flows down to take its place, even. ' tually gets hotter still, and itself rises; while the part first heated then flows to the bottom again. This process is repeated, and sets. up a

continuous current flowing to the top from the heated spot, and then down the sides and inwards towards that spot. In this way ocean currents ana winds arise. The earth being hottest at the Equator, the air there is always rising, and air from the cooler parts of the earth rushes in from the direction of the Poles to take its place. But for the revolution of the earth through space at high speed there would be 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 the cold air coming in from the outsido to take the place of. hot air that has risen up the chimney. v 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 top and tlie other to the bottom of the boiler. The hot water rises to the top of the boiler through the pipe to the cis. 1 tern through the other pipe to the bottom of the boiler giving a continuous circulation of the water through the 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.”