Page:The American Cyclopædia (1879) Volume XVI.djvu/558

 538 WEIGHTS AND MEASURES to have been in use from very early times. The Greeks, as appears from the Parian chron- icle, believed weights, measures, and the stamp- ing of gold and silver coins to have been alike the invention of Phidon, ruler of Argos, about the middle of the 8th century B. C. The units or counterpoises to be employed in weighing could easily be obtained by taking roughly equal bulks of some substance of nearly constant den- sity, as iron or brass ; but to render them more definite and accurate, it became necessary to call in the aid of more accurate measures of capacity ; and a known volume of pure water and at known density is now the criterion uni- versally resorted to for determining standards of weight. This supposes that the volume or cubic contents are correctly known ; and as we can practically only express content or ca- pacity in terms of the cube of a length, and area in terms of the square of a length, it follows that, to obtain exact units of measure of all the kinds here to be considered, it is necessary first to fix, and to be able to repro- duce with the utmost possible exactness, the unit of length. The weight of bodies in the air is slightly diminished by the buoyancy of the medium, and that of all bodies upon the earth by the centrifugal tendency due to its rotation, as well as by increase of elevation above the sea level, as in ascending mountains ; but since of these three disturbances the last two affect the article weighed and the counter- poise in the same degree, and the first also if their form and volume be the same, while the difference it can occasion in the result is ex- tremely slight in any case, it follows that in weighing ordinary articles with scales or steel- yards, the true weight is still shown under all conditions of the kinds named, or at the least to within an extremely small fraction. But weight determined by stretching or compress- ing a spring, aa in the spring balance, will be strictly proportional to the force of gravity taking effect at the place, and hence will be lessened by the increased centrifugal force as we approach the equator, and by the diminish- ing attraction at heights considerably above the sea level. In the history of weights and measures, three periods distinctly present them- selves: the ancient, or that in which the clas- sical standards were employed, ending with the decline of the Roman empire ; the middle, during which, while the names of the classi- cal measures were in many instances pre- served, the standards were lost, and the vari- ous national measures of Europe grew up; and the modern period, beginning near the close of the 16th century, and marked by the attempts made toward correcting the variable- ness found in the measures of most nations, and to attain to exact standards through a knowledge and application of physical princi- ples. Among the earlier measures of length of various nations are found such as the finger's length, the digit (second joint of the forefin- ger), the finger's breadth, the palm, the span, the cubit (length of forearm), the nail, the orgyia, (stretch of the arms), the foot, pace, &c. ; and the names of these measures, their almost constant recurrence among different nations, and the close approximation in length of such as have, like the foot, more nearly acquired the character of arbitrary measures, alike establish the fact that, in its origin, measurement of lengths was by the application of parts of the human body. In some parts of the East the Arabs, it is said, still measure the cubits of their cloth by the forearm, wjth the addition of the breadth of the other hand, which marks the end of the measure ; and the width of the thumb was in like manner for- merly added at the end of the yard by the English clothiers. Advantages of such mea- sures for popular use are, that they are mag- nitudes known by observation and readily un- derstood, and in an average way always capa- ble of being recovered, when more arbitrary standards might be wholly lost. But their great disadvantage is extreme variableness, especially when directly applied ; and in the gradual progress of men's minds toward exact- ness of conception and reasoning, though the precise period of the first of these may not now be known, three successive plans of in- suring greater accuracy have presented them- selves, and two at least have secured perma- nent adoption. The first is that of obtaining a uniform standard by exchanging the mea- sures by parts of the body for conventional or arbitrary lengths which should represent their average, and which were to be established by law ; and this point was doubtless reached at the same time among the Greeks and Romans. In England, arbitrary standards appear to have been known and in common use at an early date. The names "grain" occurring in troy weight, and " barleycorn " in long measure, show what were in that country the originals or natural units resorted to in forming these measures ; or at the least, what were the nat- ural objects chosen as the means of fixing the value of such measures. A statute of Henry III. (1266) enacts "that an English penny, called the sterling, round, without clipping, shall weigh 32 grains of wheat, well dried and gathered out of the middle of the ear ; and 20 pence [pennyweights] to make an ounce, 12 ounces a pound, 8 pounds a gallon of wine, and 8 gallons of wine a bushel of' London, which is the 8th part of a quarter." Again, Edward II. (1824) provides that the length of 3 barleycorns, round and dry, shall make an inch, 12 inches a foot, &c. The diffi- culty of determining how much of the end of the grain should be removed to render it " round " makes this standard the less definite of the two. No record exists, however, of the actual construction of standard units based upon the above definitions in grains and bar- leycorns. In comparisons of the recorded re- sults of measurements in different countries of Europe, and at different periods, much con-