BRITISH STANDARDS OF WEIGHT

Evening Star, Issue 21093, 4 May 1932, Page 14

BRITISH STANDARDS OF WEIGHT

FROM KING’S ARM TO MB LENGTH

The decennial ox ami nation of the British standards of weight and measurement was recently commenced at the National Physical Laboratory, Teddington. The Imperial standard yard (a bar of gunmetaP and the Imperial standard pound (a cylinder of platinum), which are immured in a wall of the House of Commons on the side of the staircase leading to the committee rooms, will not be disturbed, as they aro not due for examination till 1942. but the four replicas will undergo the tost. These replicas are held by the Board of Trade, the Royal Mint, the Royal Society, and the Royal oservatory. The observations will take about nine months. All our weights and measures (states a writer in 'The Times’) depend in the last resort on the two pieces of metal, but the standards themselves vary with the passage of time. The yard is getting shorter and the pound 'lighter. After the last examination in 1922 the yard was reported to be two ton-thousandths of an inch shorter than it was in 1852, and the pound bad lost one livc-millionth of its weight. These variations do not matter, of course, in commerce, but from the scientific point of view the yard’s loss of length is becoming more and more important. “We are getting to the point when science needs to be much more accurate in this matter than it used to be,’’ an expert at the National Physical Laboratory explained to me. “ The standard'of accuracy required in engineering lias gone up enormously. For instance, makers of ball bearings work to one ten thousandth of an inch. That moans they must have a gauge of a hundred thousandth of an inch, and, in turn, we must bo able to measure accurately into the millionths. Any variation in the standard therefore makes a difference.” In 1927 a report on the standards of measurement and weight was submitted to the Imperial Conference, and contained the recommendation that the existing standards “ should be replaced by standards of greater accuracy and refinement.” Nothing has yet been evolved which might take the place of the Imperial standard pound, but, should this year’s test disclose any variation of more than theoretical interest, attention will be devoted to the possibilities of a substitute. In the meantime a good deal of research has been given at the National Physical Laboratory to the discovery of a more reliable standard of measurement, and one highly characteristic of modern science has been found—a wave length of light. The new “ yard stick ” is not tangible, but it is visible through elaborate optical apparatus which has been sot up. together with other apparatus for preserving uniformity of atmospheric conditions. “We have had it under observation for some time,” I was told, “and* we are satisfied that, under given conditions, the wave length can ho reproduced to a higher order of accuracy than the present standard yard.” This will probably prove to ho the official ‘‘ yard stick ” of the future. The first standard yard, it may be added, was called an ulna or an ell, and was the length of tho arm of King Henry t.