MEASURE. 



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. Huygens proposed 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- 

 th} or' 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 objection 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 useful 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 im- 

 proved upon them, and invented sorcu 

 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," Sec. Mr. \\hite- 

 hurst 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 arc- 

 in the ratio of two to one, and of lengths 

 agreeing with the English standard in 

 whole numbers. 



To explain our philosopher's inten- 

 tions more fully, let us admit the suppo- 

 sition, that the length of a pendulum vi- 

 brating seconds in the latitude of London 

 is 39.2 inches ; the length of one vibrat- 

 ing 42 times in a minute amounts to 80 

 inches ; by the same unerring rule, ano- 

 ther vibrating 84 times in a minute musi 

 be 20 inches : the difference resulting 

 from these data is 60 inches and his pro- 

 posed standard measure. Pursuing hi? 

 experiments to the very acme of perfec- 

 tion, he found the variation in the length 

 of the two pendulums to be 59.89L* 

 inches, instead of 60, arising from an er- 

 ror in the assumed length of the second'?- 

 pendulum. 



It is generally admitted, that M:- 

 Whitehurst has succeeded in his design., 

 and demonstrated to the learned how an 

 invariable standard may at any time be 

 found for the same latitude. Besides 

 this discovery, the world is indebted to 

 him for the accurate ascertaining of a fact 

 of very considerable importance in natu- 

 ral philosophy. A person who wrote 

 with ability on this point observes, witl, 

 respect to the fact just mentioned, " Tlu- 

 difference between the lengths of UK 

 rods of two pendulums, whose vibrations 

 are known, is a datum from which may 

 be derived the true lengths of pendulums, 

 the spaces through which heavy bodies 

 fall in a given time, with many other par- 

 ticulars relative to the doctrine of gravi- 

 tation, the figure of the earth," &c. Mr. 

 "Whitehurst perceived from this experi- 

 ment, that the length of a second's pendu- 

 lum, vibrating in a circular arc of 3 20', is 

 very nearly 39.1 19 ; but performing the 

 same motion in the arc of a cycloid, the 

 result would be 39.136 inches ; conse- 

 quently, weighty substances will descend 

 in the first second after they are detached 

 from their support nearly 16.094 fact, 01- 

 16.1-|- inch. 



