STANDARD. 



munications of fir George Shuckbuigh Evelyn, in the Phi- 

 lofophical Tranfadions, deferve particular notice, as Tery 

 fcientific and accurate. Plans too liave been propoled in par- 

 liament, and though not adopted, are well worthy of being 

 recorded, as fuch may prove ufeful on future occafions. 



In 1789, fir John Riggs Miller moved for a committee 

 of the houfe of commons " to invelligate and report on the 

 beit means of adopting an vmiformity of weights and mea- 

 fures." He fuggelted the propriety of adopting the pen- 

 dulum as the Itandard of Imear extenfion ; but the fubjeft 

 was not refumed the next fcflion. The plan, however, was 

 ftrongly recommended by a pubhcation of the Rev. George 

 Skene Keith, who propofed the decimal fyflem, which was 

 foon after eilablifhcd m France. 



In 1814, fir George Clerk moved for a feleft committee 

 of the houfe of commons " to enquire into the original 

 ftandards of weights and meafures, &c." And, in order to 

 obtain information as to what were the bed means of com- 

 paring linear meafures with fome invariable natural ftandard, 

 the committee examined profeffor Playfair and Dr. W. 

 Hyde Wollaflon. Their report on the occafion contains 

 much ufeful and imp; rtant information ; and a bill founded 

 on it was brought into parHament. The plan was well re- 

 ceived, and in the beginning of the prefent year, (1816,) 

 the bill palled the houfe of commons without oppofi- 

 tion, but was lolt on the fecond reading in the houfe 

 of lords. 



The chief objeft of this bill was to aboli(h all the prefent 

 meafures of capacity, except coal meafure, and to adopt one 

 ©nly in th.'ir (lead. The propofed itandard gallon was to be 

 afcertained by weight ; that is, when filled with pure water 

 at a temperature of 62°, it was to weigh 10 lb. avoirdupois, 

 and this Itandard was deduced from the weight of a cubic 

 foot of pure water, which had been found to weigh, at the 

 fame temperature, 1000 ounces avoirdupois. Hence the 

 propofed gallon was to meafure 276.48 cubic inches. It 

 was likewife propofed to make the avoirdupois, infteid of 

 troy weight, the itandard for regulating weights; and to ad- 

 iuft the long meafures by the length of the pendulum. 

 (Other particulars of this bill, as well as the report of the 

 committee, may be feen in the Appendix to Kelly's Me- 

 trology.) . . . , 



The committee, not feeming fatisfied with the experiments 

 hitherto made on the pendulum, referred the confidcration of 

 the fubjeft to the Royal Society, who have ordered a new 

 meafurement of it to be made. This operation is now in 

 progrefs, under the direiflion of a committee, who have 

 felefted three members for the performance : namely. Dr. 

 Young, Dr. WoUafton, and Mr. Troughton. Since thefe 

 experiments have commenced, the earl Stanhope has moved 

 in the houfe of lords, that an addrefs fhould be prefented to 

 the Prince Regent to appoint a committee of fcientific men, 

 to be felefted from the univerfities and mathematical inftitu- 

 tions, to determine on the belt ftandards for an improved fyf- 

 tem of weights and meafures. 



From fuch a co.operation much may be expefted, and we 

 hope to have an opportunity of itating important refults in 

 our article Weight. At prefent, we (hall proceed to (hew 

 what has been hitherto effefted in feeking invariable Itand- 

 ards from nature, and as the purpofe of thole refearches 

 is of a popular nature, we (hall endeavour to be as ele- 

 mentary and minute as the fubjeft will admit. 



Jnvariabk Standards from Nature. — If arbitrary ftandards 

 could be preferved uniform, they would anfwer all the 

 ufeful purpofes for which they are intended ; but as all ma- 

 terial fubftances are liable to decay, methods have been 

 propofed for obtaining ftandards from fome unalterable 



property of nature, by which loft meafures might be tC' 

 llored, or new fyftems eftabliftied : but it is remark- 

 able that, in deducing ftandards from nature, nature 

 oppofes many obftacles difficult to be furmounted. 

 Among the different methods that have been fuggelted, 

 two only have been purfued with any degree of fuccefs, 

 namely, the length of a pendulum that vibrates feconds of 

 mean time ; and the length of an arc or portion of the me- 

 ridian. If the earth had been a perfeft fphere, thofe mea- 

 fures might be obtained without much difficulty ; but it is a 

 kind of oblate fpheroid, having its equatorial diameter 

 longer than its axis or polar diameter. Hence the gra- 

 vity of bodies varies on its furface, in proportion to their 

 diftance from the centre of the earth ; and, therefore, a pen- 

 dulum muft be longer at the poles than on the equator, in 

 order to vibrate equal portions of time. From the fphe- 

 roidical figure of the earth, too, the degrees of the meridian 

 vary, increafing in length, hke the pendulum, from the 

 equator to the pole. In order to afcertain thefe variations, 

 many calculations and meafurements have been made by the 

 greateft mathematicians ; and yet, with all their accumu- 

 lated labours, up to the prefent time, the folutions are un- 

 fatisfaftory. " It appears," fays Laplace, in his Syfteme 

 du Monde, " that the earth differs fenfibly from an ellip- 

 foid : there is alfo reafon to believe that its two hemi- 

 fpheres are not equal on each fide of the equator." Doubts 

 are hkewife entertained of the uniformity of gravitation in 

 different longitudes, though in the fame latitude ; and alfo 

 of the equality of degrees of the meridian in thofe fituations. 

 The ratio, therefore, of any portion of the meridian to the 

 whole circle is uncertain. 



According to fir Ifaac Newton's theory, the equatorial 

 diameter is to the polar as 230 to 229 ; or, in other words, 

 the earth's ellipticity is ^i^. This computation was made 

 on the hvpothefis, that the earth is an homogeneous ellipfoid j 

 but on the fuppofition that it is heterogeneous, the ellipticity 

 or oblatenefs is found to be lefs, as may be feen by the 

 tables contained in this article. 



The meafurement of a degree of the meridian was at- 

 tempted at a very remote period by the Egyptians, as 

 already noticed ; but from the rude and imperfeft ftate of the 

 mechanical arts in ancient times, great doubts muft be enter- 

 tained of the accuracy of fuch operations. With refpeft to 

 the pendulum, it was not known to the ancients ; but it has 

 greatly engaged the attention of modern aftronomers and 

 mechanifts, as well as the meafurement of the meridian. 

 For a particular account of both, fee our articles Degree, 

 E.\RTH, and Pesdulu.m. 



Huygens was the firft who propofed the pendulum as 

 the itandard for linear meafure ; that is, its length from the 

 point of fufpenfion to the centre of ofcillation. Tiie third 

 part of this diftance he termed the horary foot, which he 

 recommended to be the univerfal ftandard : but the varia- 

 tions of its length in different latitudes, as well as the great 

 difficulty of obtaining the exaft meafurement, above ftated, 

 feemed to condemn tnis plan as wholly imprafticable. The 

 fame ingenious philofopher propofed the method of ob- 

 taining tlie length of the pendulum by means of a rectan- 

 gular cone ; which when fufpended by its vertex, and made 

 to vibrate, the centre of its bafe he demonftrated to be the 

 centre of ofcillation, and reciprocally, if fufpended by the 

 centre of its bafe, its vertex would be the centre of ofcilla- 

 tion, fuppofing, in both cafes, that the length of the 

 ifochronous fimple pendulum was equal to the altitude of 

 the cone, or the femidiameter of the bafe. He likewife fug« 

 gefted, as an invariable ftandard of length, the fpace that a 

 heavy body would fall through in a fecond of time ; but 



this, 



