Science Lecture.

Wairarapa Standard, Volume XIX, Issue 1845, 16 June 1886, Page 3

Science Lecture.

(Continued). Hiring dealt with the natural and artificial sources of beat, we shall now take np the effects of heat. One of the most easily observed effects of beat on matter in all states hj that of causing expansion, forcing the atoms farther from each ether, so that the rolame of the body is increased. Beginning with solids, there are several very simple experiments to show the expansion of metals, especially under the influence of heat. Exp. 10. This simple piece of apparatus made of the rib or spoke of an old umbrella is so arranged that any expansion of the short wire will cause the long rib or index to move to the right. Note that at present the index is exactly in front of this line on the cord behind the index. Now when the heat of a spirit lamp is applied yon notice how rapidly the index chows that the heated rod is expanding. Now that the index has moved considerably to the right I cool the rod with water, and immediately the index returns to its original position.

One familiar application of this property of iron is olten seen at the wheelwright’s when a tire is to be fitted to a cart wheel The iron lire is made a little too small to go on to the wooden frame of tbe wheel. Then after the tire baa been heated till it expands, it is plated on the framework, and quicklycooled with water. The consequent con traction fixes the tire more satisfactorily than any other pricers. Similarly when the wall of a luilding has left the perpendicular it is possible to bring it right again by the application of this principle. he wails that are to be brought op are connected by iron rods, on the ends of which note can be screwed. The rods are heated, and the oats screwed np to the outside of the wall. The cooling and contraction of tbe rods pnlla np the walls toward their proper position, and by repetitions! of this process the walls may be again made nprigfit, and secured firmly. Exp. 11. The ball and ring experiment is ■imply a modification of the last experiment. A ball and ring of metal are so made that tbe ball will jnst pass tbrongh tbe ring at ordinary temperatures. Heat the ball, and it ii found impossible to pans it through tbe ring, as tbe ball has expended. fitted tightly in tbe neck of a bottle and heated will, by iU expansion, burst the neck of the bottle. It is matter of common observation that telegraph wires expand in hot weather, for they are aeen then to sag or form long earns beeween tbe posts, instead of being tease. Taking now the expansion of liquids by beat, it has been already shown in Exp 1 of Lecture HI that water expands under the influence of beat. Then, as now, I used tbie instrument, which we may call a water thermometer. Exp. 13. This is simnly a flack filled with colored water, and fitted with a cork, perforated by along upright gl-gg tube. When the water in the fia.k i. heated, the expansion of tbe water is shown hy its rise i;i the tube. The expansion of the liquid mercury under the influence of heat is of the greatest importancs enabling us to construct that useful instrument tl e common thermometer. Tbe principle is exactly the same as that of the water thermometer, a graduated scale serving to mark tbe expansion of the mercury when heated. Exp. 15. A ntber striking experiment, showing that water expands when heated, is as follows Half till a glass dish with cold water, and float on its surface a piece of card. Then pour into the vessel boiling water colored with some dye, directing the stream Upon tbe eard. The cob red boiling water which has expanded, and is therefore lighter boik for balk than tbe cold water, will remain for a time as a distinct layer floating on top of the cold water.

The expansion of gases by heating has already been shown in the case of air, which is a mixture of gases, Exp. 3 to 12 in Lecture I. There is au easily constructed instrument called the sir thermometer, which ii very •eositive to heat, and it is indeed tbe original torn of thermometer. Exp. 16. A bulb or flask fitted with a very lung and narrow tnbe, aud partly filled with air, baa tbe month tube dipped in water. On applying a warm hand to tbe bnlb the ait contained expands, and forces down tbe ••ter in the tnbe. II the water be colored, then ite motion in the tnbe ie more easily Ren, **P* 17. A dry bladder blown np with air, ud tied lightly at the mouth will burst if Mated strongly. Children often bring from the seashore tbe bladder* or floats of sea •ceda in older to enjoy tbs noise caused by •Met tasting when placed near the fir*. 18- The experiment of lending np a fire balloon, already explained in Exp. 9 of “ta I. chew* for nir what experiment 15 “ *ta lecture shows for water, that is, that Ih* bested flnid is lighter bulk, for bulk, than m* Mlic« fluid, tending to rise above it •ad that therefore air expands with heat.