താൾ:CiXIV132a.pdf/370

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LVIII

very useful. Both are placed horizontally and the maximum
thermometer, whilst rising, pushes a small piece of iron wire,
which will remain on the highest point as soon as the mercury
contracts. The minimum thermometer contains a very small
hollow glass, which is not displaced as long as the alcohol ex
pands, but which in consequence of adhesion is carried with the
alcohol as long as it contracts.

§ 142. 2) A very instructive example of Expansion is
Gravesande's ring. It is a brass-ball, which in ordinary tem
perature passes freely through a ring, but when heated, does not
pass through. For another example see Physics Primer, page 64.

a) Expansion of solids:

§ 142. As to the linear expansion of a body in heating it
from 0-100°C we ascertain what part of its length is added by
expansion. The number representing this is called the Coeffici
ent of expansion. The length of a body being 500' at 0°C and
501' at 100°C, the Coefficient of expansion will be 1/500. The
cubic expansion is three times greater than the linear one. Every
solid body has its own coefficient of expansion (cohesion being
different with various bodies). For solid bodies expansion bet
ween 0° and 100° is in general proportional to temperature, not
so in higher temperatures and with liquids (with the exception
of mercury). Examples:

Securing tires on wheel. 289. Iron roofing not to be solder
ed, 294 (railways); hot water poured in a tumbler. 293. The
walls of a gallery at the Conservatoire des Arts et Métiers in Paris
began to bulge and were drawn together by passing iron bars
through them; the bars were exposed to heat, expanded and
were screwed up, allowed to cool they contracted and drew the
walls together. Another application is the Compensation Pen

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