As to Thermometers.

Auckland Star, Volume XXII, Issue 139, 13 June 1891, Page 3 (Supplement)

As to Thermometers.

The aperture in the tube of a thermometer is smaller than the finest hair. Though ib appears bo be round, it is not; if it were, the mercury could nob be easily seen. Ib is, bherefore, made flab, and bhen bhe glass magnifies ib so bhab ib seems to bequitelarge. To bring ib oub sbill more disbincbly, a maker of Boßbon recently conceived the idea of backing the tube wibh a bhin film of whibe sizing. This device is now generallyadopted by the foreign makers. Mercury is generally used in thermometers because ib is more regular in ibs contractions and expansions. Ib is, indeed, impossible to make a spirit thermometer that will be as trustworthy as one in which mercury is used. In a mercurial thermometer the degree marks are all the same distance apart, because the expansion under all conditions is uniform ; bub in a spirit thermometer the degrees are wider apart at the top, because the expansion increases ab a greater ratio after a certain temperature is reached. Though not so trustworbhy, spirit thermomebers are necessary, as mercury freezes ab forty degrees below zero. Spirits of wine is generally used, and is coloured red, so thab ib will be more visible to the eye.

In a correct thermometer, the scale is graduated to the requirements of bhe tube to which ib ia fibbed, so thab every correct thermometer must have a special scale of ibs own. Thab is bo say, ib wouldn't do to put bhe bube of one thermometer in bhe frame of another. Of course, in the very cheap grades of thermometers such accurate adjustments are not made, and, therefore, their records are only approximately correct. The besb thermometer tube made will cost about five dollars; bub a thermometer may be made to cost almost any price, according bo bhe way in which ib is mounted."

As everyone knows, the Fahrenheib scale is thab mosb commonly used in bhis counbry. Fahrenheib arbitrarily assumed a limib of cold which he termed zero. This makes the freezing point .hirby-two degrees above zero and bhe boiling poinfe bwo hunand twelve degrees above zero. As a matter of fact, however, in northern latitudes the temperature in winter frequently falls below the zero point, so that there is no scientific reason why the zero point in the Fahrenheit scale should be where ib is. A much more scientific scale is bhab known as the cenbigrade, which marks the point at which water freezes as zero, and divides the space between thab and bhe poinb ab which waber boils into one hundred degrees. In bhe Reaumur scale zero marks the freezing poinb and eighby above zero bhe boiling point. Many eelf-regisbering bhermomebers are. now used. These inetrumenbs mark the highest or lowest temperature reached, as bhe case may be, so bhab one may return at nighb feeling assured bhab bhe weather can play no pranks wibhou. his learning of them. — ' Scienbific American.'