MEASURE of a figure or a surface per fectly level, thence called a plane surface, is a square inch, foot, or yard. This square is termed the measuring unit, be cause the side is an inch, a foot, a yard, or any other determinate extent.
MEAsuns of a certain portion or quantity of matter, is its weight.
MEAsuns of a number, applies thus : 2 is the measure of 4, 3 of 6, &c.; in fact, it is any number which divides without are minder.
It has long been wished by the learn ed, that an universal measure, secured by penalties in an unalterable state, hal hitherto been, or may hereafter he adopt ed, which would prove of incalculable.. advantage to mankind in their philosophi cal and even less exalted pursuits. Pre judices are, however, far too numerous and powerful to he easily overcome, or removed, in matters of infinitely less mo ment. We Cannot, therefore, entertain the slightest hope that national partiality will be subdued in every quarter of the globe, so as to produce a general resigna tion of favourite methods, in order to adopt a new one recommended by a con-, gress of philosophers, which it would be equally difficult to assemble, or prevail upon to agree to any plan unanimously. The theories of eminent men on this sub ject .are useful and deserve attention, as they may suggest improvements of great importance. Huygensproposed the length of a pendulum that should vibrate se conds, to be measured from the point of suspension to that of oscillation. The third part of this pendulum he termed a horary foot, and such he recommended should be the standard by which the mea sure of every foot in Europe might be re gulated. Admitting his plan to be wor thy of adoption, and an experiment made, it appears that the Paris foot would bear a proportion to the horary foot of 864 to 881, which is demonstrated in this man ner: The length of three Paris feet is 864 half lines, and that of a pendulum vi brating seconds consists of 881 half lines. The principal abjection to this ingenious suggestion of Huygens is founded on the assumption, that the action of gravity is the same in all parts of the globe, which is certainly not the case ; consequently, instead of its serving universally, it would be useffil only in those places which lie under the same parallel of latitude. Thus,
if each different latitude had its foot equal to the proposed third part of the pendulum vibrating seconds there, any given latitude must have a different length for the foot. Exclusive of this ob jection, there would be a second pro ceeding from the difficulty attending the exact measurement between the cen tres of motion and oscillation, which is such, that it is highly probable no two persons would agree in their accounts of the space.
Many attempts and expedients were suggested, after the rejection of the above plan, with similar want of success. This circumstance did not escape the notice of the Society for the Encouragement of Arts, Manufactures, and Commerce, the officers of which, with a commendable zeal, advertized a premium of one hun dred guineas, or a gold medal, as a re ward to those who would propose the ap proved means " for obtaining invariable standards for weights and measures, com municable at all times and to all nations." This invitation produced a communica tion from Mr. Hatton, in 1779, in which he proposed the application of a movea ble point of suspension to one and the same pendulum, and by this means he in tended to accomplish the full effect of two, the difference in the lengths of which was the desired measure.
The ideas of Mr. Hatton were approv ed by the ingenious Whitehurst, who i• proved upon them, and invented some very curious and excellent machinery ; besides which, he published, eight years after, a work entitled " An Attempt to wards obtaining invariable Measures of Length, Capacity, and Weight, from the Mensuration of Time," he. Mr. White burst thought it convenient and proper, for attaining this most desirable end, to endeavour to obtain a measure of the greatest convenient length from two pendulums, the vibrations of which. are in the ratio of two to one, and of lengths agreeing with the English standard in whole numbers.