WEIGHTS AND MEASURES. The subject of weights and meaeures is one the actual state of which is prosperous in the inverse ratio of the number of books or the length of articles which are written upon it. There is nothing iu it which might not, if the most natural and simple system were adopted, be described in a very few pages. We are speaking of course only with reference to a possible time ; for, let that time arrive when it may, the history of the past must be a confused and repulsive subject..
' In the article WEIGHT, &G., STANDARD OF, we shall give some idea of the recent history of the attempts which have been made in England to secure a permanent measure of length. These have only succeeded, at least until very recently, somewhat farther than to the extent of making it poesible to restore to the merchant a system sufficiently near to that which now exists, if the latter should be lost ; but they have all confessedly failed in perpetuating (sufficient exactness for scientific purposes. The same may be said of the French endeavour to 'create a recoverable standard by the measurement of the earth. [TRIGONOMETRICAL SURVEY.] So that in fact we are now come back again to the old notion, that tho true way to maintain a measure is to construct accurate copies out of durable material, and to preserve those copies with care.
The measures of time (of which we speak more particularly in Yren, Tree, Pearons or ItevostrrioN) are the only usual ones in which a natural standard exists; to which wo may add, that in the kindred operation of counting there is something of the same kind. The phenomena of the daily revolution of the earth, and the ten fingers on the two hands, have secured to the whole human race, above the degree of the lowest savages, one mode of assigning periods of duration and large collections of number. But even in these two subjects details have differed considerably in different times and countries; and much more has this happened with respect to measures in which the choice of a standard is purely arbitrary, as in the case of length, surface, capacity, and weight. The angle is another magnitude which has a natural measure [Aects); and, as this has never been out of the hands of geometers, a greater uniformity has prevailed in the measurement of angular magnitude than of any other whatsoever. The measures of
length obviously regulate those of surface and capacity. There is no other way of defining an area or a solidity, except by describing, for the area, lengths, and for the solidity, surfaces, by which the area or solid may be bounded in a given manuer. Measures of weight may be obtained by defining, as standards, given bulks of given substances ; and as water is the most common and most easily purified of all substances, It has been chosen by common consent as the referee for such standards. A usseurure of length then is all that is wanted in the first instance ; and most nations, micient and modern, have been in the habit of referring all the resulting measures to those of length alone. Nevertheless, there is no small difficulty in obtaining a comparison of a measure of weight deduced from length with one already existing, in such a manner as to perpetuate the latter, if the utmost accuracy be required. (hater,' Construction and Adjustment,' &c.,' Phil. Trans.,' 1826.) So that the commissioners who last reported on the subject advise thet the standard of weight shall no longer be deduced from that of length, but shall bo simply a piece of metal or other durable substance.
It is not our object In this article to consider weights and measures in a scientific point of view, but simply to give some historical account of the measures actually in use, and some tables of the principal ones, ancient and modern. There is no subject whose history is more dis tinctly divided into three periods, ancient, middle, and modern, than that of weights and measures. The ancient period, ending with the decline of the Roman empire, during which the classical standards were preserved and employed; the middle period, during which, while the names and relations of the classical measures were preserved among the learned, the standards were lost, and the various differencem of national measures began to exist among the people ; the modern period, which hardly begins before the 17th century, in which the discrepan cies of national measures were noted, and the attempts at a system founded upon natural philosophy began to be made.