WEIGHTS AND MEASURES, STANDARD. In this article we separate from the general subject of WEIGHTS AND MEASURES those preliminary considerations which refer to the manner in which weights and measures are verified and preserved, so far as they can be entered upon in a work partly of reference, partly of general information. We do not pretend to complete a scientific account, but shall bo satisfied with preparing the unpractised reader to look with some degree of interest on the sources of more elaborate information to which we shall refer.
Measures are wanted for two distinct objects, the commercial and the scientific. The wants of natural philosophy have grown up within the last two centuries; while so early as Magna Charts it was one of the concessions to the grievances of the subject that there should be one weight and one measure throughout the land. But though a few acts of parliament were sufficient, in process of time, substantially to establish the political rights which that charter was intended to grant, hundreds of them, down to the present time, have been ineffectual in producing the use of one weight and one measure. Some of these we shall afterwards refer to [WEIGHTS, Zsc.] • in the meanwhile we have here only to state that, as may be this unity was for com mercial, not scientific purposes ; and that the resemblance of natural objects was !supposed to be a sufficient reliance for obtaining it. Some of the old statutes expressly make the inch to be the length of three barleycorns, placed end to end, round and dry, from the middle of the ear. Standards were made, no doubt, from this definition; or at least it was supposed that if the existing standard should be lost, the barley corns would enable its restoration to be effected. Our readers may smile at what they think so rude a contrivance ; but the same prin ciple, carried a little further, might be made very efficient in preserving a measure. Suppose for example, that the government were now to think it desirable to recover the three-barleycorn inch, or at least to invent one which should be capable of being recovered. They,would
put together not three barleycorns, but three thousand, or thirty thousand; or many different collections of three thousand or more. The average inch deduced from these would be capable of being re covered at any time from the same grain grown in the same eeil. A commercial standard might be easily recovered from many different modes of proceeding : for example, the average height of the barometer at a given place throughout any period of five years is so nearly the same from one five years to soother, that a commercial standard might be sufficiently well obtained from it. It would be of little consequence if the yard were wrongly recovered by one-hundredth or even one tenth of an inch, in any matter of buying and selling.
It is the scientific standard at which the government has been aiming during the last century. The object here is, first, to measure the old standards to the utmost accuracy of which our senses, assisted by microscopes, are capable; secondly, to discover the means of recon structing a lost standard. In the more delicate operations of natural philosophy and astronomy, our knowledge cannot go down to posterity, unless they know within the thousandth of an inch what it is that we call a yard. The public at large has never understood the reason why so much trouble has been taken ; and perhaps the members of different administrations, while trusting such investigations to men of science, and relying on them for the whole conduct of the matter, may have wondered at the great difficulty which there seemed to be in the way of furnishing the shopkeepers of all generations with the yard measures and pound weights of the same values. It is our principal object in this article to endeavour to point out the nature of these difficulties, and the extent to which they have been overcome : it being remem bered however that the object is scientific, not commercial, and that the standard of length is chosen as the most important illustration.