Weights and Measures

We measure length, capacity and weight and use standard units in these cases. The principal early standards of length were the palm or hand breadth, the foot and the cubit, which is the length from the elbow to the tip of the middle finger. Such standards were not accurate and definite. Only in modern time people adopted unchanging standards of measurement.

In the English-speaking world, the everyday units of linear measurement were traditionally the inch, foot, yard and mile. In Great Britain people defined these units of length in terms of the imperial standard yard, which was the distance between two lines on a bronze bar made in 1845.

In Britain scientists now also derive units of weight (ounces, pounds, and tons) from the metric standard — kilogram. This is a solid cylinder of platinum-iridium alloy maintained at constant temperature at Sevres, near Paris.

National standards laboratories in many countries maintain copies of this standard as exact as possible.

International System of Units is a system of measurement units based on the MKS (meter-kilogram-second) system. This international system is commonly referred to as SI.

At the Eleventh General Conference on Weights and Measures that took place in Paris in 1960 scientists defined standards for six base units and two supplementary units.

Length

The meter had its origin in the metric system. By in­ternational agreement the scientists defined the standard meter as the distance between two fine lines on a bar of platinum-iridium alloy. The 1960 conference redefined the meter as 1,650,763.73 wavelengths of the reddish-orange light that the isotope krypton-86 emitted. The scientists again redefined the meter in 1983 as the length of the path that light in a vacuum traveled during a time interval of 1/299,792,458 of a second.

Mass

When scientists created the metric system, they defined the kilogram as the mass of 1 cubic decimeter of pure water at the temperature of its maximum density or at 4.0 °C.

Time

For centuries, we measured time universally in terms of the rotation of the earth. The second is the basic unit of time. Scientists defined it as 1/86,400 of a mean solar day or one complete rotation of the earth on its axis in relation to the sun. They discovered, however, that the rotation of the earth was not constant enough to serve as the basis of the time standard. As a result, scientists redefined the second in 1967 in terms of the resonant frequency of the caesium atom, that is, the frequency at which this atom absorbs energy.

Temperature

The temperature scale is based on a fixed temperature, that of the triple point of water at which it's solid, liquid and gaseous. Scientists designate the freezing point of water as 273.15 K. It equals exactly 0° on the Celsius temperature scale. The Celsius scale, which is identical to the centigrade scale, gets its name from the name of the 18th-century Swedish astronomer Anders Celsius. He first proposed the use of a scale in which the interval between the freezing and boiling points of water is divided into 100 degrees. By international agreement, the term Celsius has offi­cially replaced centigrade.

One feature of SI is that some units are too large for ordinary use and others too small. To compensate, scientists borrowed and expanded the prefixes for the metric system. Examples are millimeter (mm), kilometer/hour (km/h ), megawatt (MW), andpicofarad (pF). The prefixes hecto, deka, deci, and centi are used only rarely, and then usually with meter to express areas and volumes.

aqua regia - королевская водка

plating - покрытие

long-lasting - долговечный

crystallography - кристаллография

to be referred to as - называться

ruby - рубин

acids - сульфонаты

melting point - температура плавления, точка плавления

radio tube - электронная лампа

gold-based - основанный на золоте

machine-tool - станок

solid - твердый

workpiece - обрабатываемая деталь

cutting tool - режущий инструмент, резец

thread - резьба

full-time, part-time, external students - студенты дневного, вечернего, заочного отделений

to be equipped - быть оборудованным

up-to-date - современный

made - сделанный

to be referred to as - называться

is based - основан

fixed - фиксированный

triple point - тройная точка

is divided -поделен

has offi­cially replaced - официально заменил

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