MEASURE. 



Dr. Young-, to whom we acknowledge 

 ourselves indebted for many of the follow- 

 ing particulars, has given an excellent 

 compressed table of measures and stand- 

 ards, in his recent valuable work, " A 

 Course of Lectures on Natural Philoso- 

 phy," &c. from which we find, that the 

 English yard is said to have been derived 

 from the lengtii of the arm of Henry I. in 

 the year 1101 ; that Graham asserts the 

 length of the pendulum vibrating seconds 

 accurately is equal to 39-13 inches ; that 

 Bird's parliamentary standard is admitted 

 to be of the greatest authority, and that 

 it agrees nearly with the scales of Shuck- 

 burgh and Pictet, made by Troughton. 

 The standard of the Royal Society by 

 Graham exceeds that of Bird's in length 

 about 1000th part of an inch, but it is not 

 quite uniform throughout its length. The 

 standard in the Exchequer is about .0075 

 inch shorter than the yard of the Royal 

 Society. General Roy used a scale of 

 Sisson, divided by Bird, and found it to 

 agree exactly with the Tower standard on 

 the Royal Society's scale. Sir George 

 Shuckburgh, adopting Trough ton's scales 

 for the standard, found the original Tow- 

 er standard 36.004 ; the yard E. on the 

 Royal Society's scale by Graham 36.0013 

 inches ; the yard Exchequer of the same 

 scale 35.9933 ; Roy's scale 36.00036 ; the 

 Royal Society's scale by Bird 35.99955 ; 

 Bird's parliamentary standard of 1758, 

 36.00023. The English have employed 

 and adjusted their standards at the tem- 

 perature of 62 of Fahrenheit's thermo- 

 meter, and the French at the freezing 

 point of water. The French metre is 

 39.37100 English inches, and the ten mil- 

 lionth part of the quadrant of the meri- 

 dian. The same measure contains 36.9413 

 French inches, or three feet 11.296 lines. 

 Hence, says the Doctor, the French toise 

 of 72 inches is equal to 76.736 English 

 inches. One of Lalande's standards mea- 

 sured by Dr. Maskelyne was 76.732, 

 the other 76.736. In latitude 45, a pen- 

 dulum of the length of a metre would 

 perform in a vacuum 86116.5 vibrations 

 in a day. The length of the second pen- 

 dulum is 993827 at Paris. 



The French National Institute of Sci- 

 ences and Arts have turned their atten- 

 tion to this subject, and in the month of 

 Nivose, in the year 1801, a member read 

 a report from a committee, founded on 

 the comparison of the standard metre of 

 the Institute with the English foot. And 

 M. Pictet, professor of natural philosophy 

 at Geneva, exhibited to the class, in the 

 month of Venderaiaire. a collection of the 



VOL. IV. 



most interesting objects, which he had 

 collected in England, relating to arts and 

 sciences. One of the number was a stan- 

 dard of the English linear measure, which 

 was of brass, 49 inches in length, and 

 neatly divided by engraved lines into 

 tenths of an inch. This standard was 

 made for the exhibitor by Troughton, a 

 resident in London, who has deservedly 

 acquired the reputation of dividing instru- 

 ments with the utmost accuracy,, which, 

 was compared with another made by the 

 same artist for Sir George Shuckburgh, 

 when it was ascertained, satis factorily; 

 that the variations between them did 

 not amount to more than the difference 

 between the divisions of each ; in -i.iier 

 words, the variation was almost imper- 

 ceptible. Arguing from this circum- 

 stance, the standard may be considered 

 as identical with that described by Sir 

 George Shuckburgh in the Philosophical 

 Transactions for 1798. 



Another excellent, instrument, con- 

 structed by Mr. Troughton, and shewn 

 at the same time by M. Pictet, was a com- 

 parer, calculated to ascertain minute va- 

 riations between measures. This instru- 

 ment " consists of two microscopes, with 

 cross wires, placed in a vertical situation, 

 the surface of the scale being horizontal, 

 and fixed at proper distances upon a me- 

 tallic rod. One of them remains stationa- 

 ry at one end of the scale, the other is oc- 

 casionally fixed near to the other end ; 

 and its cross wires are moveable by means 

 of a screw, describing in its revolution one 

 100th part of an inch, and furnished with 

 a circular index, dividing each turu inlo 

 100 parts ; so that having two lengths, 

 which differ only one-tenth of an inc-h 

 from each other, we may determine their 

 difference in ten-thousandths of an inchy 

 The wires are placed obliquely with re- 

 spect to the scale, so that the line of di- 

 vision must bisject the acute angle which 

 they form, in order to coincide with their 

 intersection." An instrument similar to 

 that thus described, and made by Rams- 

 den, for measuring the expansion of me- 

 tals, was described by General Roy in the 

 seventy-fifth volume of the Royal Trans- 

 actions. 



M. Pictet, influenced by a desire of ad- 

 vancing science, made an offer to the class 

 of the use of the standard and the micro- 

 meter, for the purpose of determining the 

 comparative length of the metre and the 

 English foot : the offer was gratefully ac- 

 cepted by the Society, and Messieurs Le- 

 gendre, Machain, and Prony, were ap- 

 pointed to assist M. Pictet in making the 



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