August 15, 1889] 



NATURE 



Ml 



those of space and time. Such a system is quite practicable in 

 astronomy, but cannot yet be applied with accuracy to ordinary 

 terrestrial purposes. According to the law of gravitation, 



Mass = Acceleration x (Distance)'^ ; 



and as in the case of the earth we can measure the quantities 

 on the right-hand side of that equation with considerable 

 accuracy, we can satisfactorily determine the earth's mass in 

 terms of the supposed unit. That sufifices for the needs of 

 astronomy, but for other scientific and commercial purposes a 

 standard of mass having a magnitude of about a pound is neces- 

 sary, and as two such masses can be compared with each other 

 froin five to ten thousand times more accurately than either of 

 them can be determined in terms of the supposed imit, three 

 fundamental units are preferable to two. 



The Chaldeans, Babylonians, Persians, Greeks, and Romans, 

 all seem to have had systems of weights and measures based 

 upon tolerably definite standards, but after the decline of the 

 Roman Empire these standards seem to have been forgotten, 

 and in the beginning of the sixteenth century the human body 

 had so far become the standard of measurement that the units in 

 common use — as, for example, the foot, palm, &c., — were 

 frequently taken directly from it. The complete table of 

 measures of length was then as follows : the breadth (not the 

 length) of four barley-corns make a digit, or finger-breadth ; four 

 digits make a palm (measured across the middle joints of the 

 fingers) ; four palms are one foot ; a foot and a half is a cubit ; 1 

 ten palms, or two feet and a half, are a step ; two steps, or five i 

 feet are a pace ; ten feet are a perch ; one hundred and twenty- i 

 five'p^ces are an Italic stadium ; eight stadia, or one thousand j 

 paces, are an Italic mile ; four Italic miles are a German mile ; ; 

 and five Italic miles are a Swiss mile. It was then the practice i 

 to furnish standards of length in books by printing in them lines 

 a foot or a palm long, according to the size of the page, and 

 from these and other data it appears that the foot then used on 

 the continent of Europe had a length of about ten English 

 inches. 



In England, the first attempts at scientific accuracy in matters 

 of measurement date from the beginning of the seventeenth cen- 

 tury, when John Greaves, who must be considered as the earliest 

 of the scientific metrologists, directed attention to the differ- 

 ence between the Roman and English foot by tolerably accurate 

 determinations of the former, and also attempted the investiga- 

 tion of the Roman weights. He was followed by Dr. Edward 

 Bernard, who wrote a treatise on ancient weights and measures 

 about 1685, and towards the end of the century the measure- 

 ments of the length of a degree by Picard and J. D. Cassini 

 awakened the attention of the French to the importance of 

 rigorously exact standards. In considering the progress of 

 science with respect to standards of length, we may safely confine 

 our inquiries to the English yard and the French toise and 

 metre, for during the last two hundred years they have been 

 almost the only standards adopted in scientific operations. 



The English measures of length have come down from the 

 Saxons but the oldest standards now existing are the Exchequer 

 yards of Henry VII. (1490) and Elizabeth (1588). These are 

 both brass-end measures, the former being an octagonal rod 

 about half an inch in diameter, very coarsely made, and as rudely 

 divided into inches on the right-hand end and into sixteenths of 

 a yard on the left-hand end ; the latter a square rod with sides 

 about half an inch wide, also divided into sixteenths of a yard, 

 and provided with a brass bed having end-pieces between which 

 the yard fits. One end of the bed is divided into inches and 

 half-inches. Francis Baily, who saw this Elizabethan standard 

 in 1836, speaks of it as "this curious instrument, of which it is 

 impossible, at the present day, to speak too much in derision or 

 contempt. A common kitchen poker, filed at the ends in the 

 rudest manner by the most bungling workman, would make as 

 good a standard. It has been broken asunder ; and the two pieces 

 have been dove-tailed together : but so badly that the joint is nearly 

 as loose as that of a pair of tongs. The date of this fracture I 

 could not ascertain, it having occurred beyond the memory or 

 knowledge of any of the officers at the Exchequer. And yet, 

 till within the last ten years, to the disgrace of this country, 

 copies of this measure have been circulated all over Europe and 

 America, with a parchment document accompanying them 

 (charged with a stamp that costs ^^3 \os., exclusive of official 

 fees), certifying that they are true copies of the English 

 standard J" 



In the year 1742 certain members of the Royal Society of 



London, and of the Royal Academy of Sciences of Paris, pro- 

 posed that, in order to facilitate a comparison of the scientific 

 operations tarried on in the two countries, accurate standards of 

 the measures and weights of both should be prepared and pre- 

 served in the archives of each of these Societies This proposi- 

 tion having been approved, Mr. George Graham, at the instance 

 of the Royal Society, had two substantial brass rods made^ 

 upon which he laid off, with the greatest care, the length of 

 3 English feet from the standard yard kept at the Tower of 

 London. These two rods, together with a set of troy weights, 

 were then sent over to the Paris Academy, which body, in like 

 manner, had the measure of a French half-toise set off upon the 

 rods, and keeping one, as previously agreed, returned the other, 

 together with a standard weight of two marcs, to the Royal 

 Society. In 1835, Baily declared this copy of the half-toise to 

 be of little value because the original loise-talon was of iron, 

 and the standard temperature in France differed from that in. 

 England. In his opinion the French should have sent over an 

 iron half-toise in exchange for the English brass yard ; but this 

 criticism loses much of its force when it is remembered that in 

 1742 neither England nor France had fixed upon a temperature 

 at which their standards were to be regarded as of the true 

 length. On the return of the rod from Paris, Mr. Graham 

 caused Jonathan Sisson to divide the English yard and the 

 French half-toise each into three equal parts, after which the 

 rod was deposited in the archives of the Royal Society, where it- 

 still remains. Objection having been made that the original and 

 legal standard yard of England was not the one at the Tower, 

 but the Elizabethan standard at the Exchequer, the Royal 

 Society requested Mr. Graham to compare his newly-made scale 

 with the latter standard, and on Friday, April 22, 1743, he did 

 so in the presence of a Committee of seven members of the Royal 

 Society. In the following week the same gentlemen compared 

 the Royal Society's scale with the standards at Guildhall and 

 the Tower, and also with the standard of the Clickmakers' 

 Company. These comparisons having shown that the copy of 

 the Tower yard upon the Royal Society's scale was about 0-0075 

 of an inch longer than the standard at the Exchequer, Mr. 

 Graham inscribed upon the Royal Society's scale a copy of the 

 latter standard also, marking it with the letters Exch., to dis- 

 tinguish it from the former, which was marked E. (English), and 

 from the half-toise which was marked F. (French). 



In the year 1758 the House of Commons appointed a Com- 

 mittee to inquire into the original standards of weights and 

 measures of England ; and, under instructions from that Com- 

 mittee, the celebrated instrument-maker, John Bird, prepared 

 two brass rods, respecting which the Committee speak as follows 

 in their Report : " And having those rods, together with that of 

 the Royal Society, laid in the same place, at the receipt of the 

 Exchequer, all night with the standards of length kept there, to 

 prevent the variation which the difference of air might make 

 upon them, they the next morning compared them all, and, by 

 the means of beam compasses brou.^ht by Mr. Bird, found them 

 to agree as near as it was possible." One of these rods was 

 arranged as a matrix for testing end-measures, and the other was 

 a line measure which the Committee recommended should be 

 made the legal standard of England, and which has since been 

 known as Bird's standard of 1758. Respecting the statement 

 that after lying together all night the rods were all found to 

 agree as near as it was possible, Baily says : " This is somewhat 

 remarkable, and requires further explanation, which unfortunately 

 cannot now be accurately obtained. For it is notorious that the 

 measure of the yard of the Royal Society's scale differs very con- 

 siderably from the standard yard at the Exchequer. . . . Owing 

 to this singular confusion of the lengths of the measures, which, 

 does not appear to have been unravelled by any subsequent 

 Committee, it has happened that the Imperial standard yard 

 has been assumed nearly i ^ 140 of an inch longer than 

 the'ancient measure of the kingdom." There is little difficulty 

 in surmising what Bird did. The Exchequer standard consisted 

 of a rod and its matrix. The Royal Society's Committee 

 assumed the rod to be the true standard of 36 inches, and upon 

 that assumption Graham's measurements gave for the length of 

 the matrix 36 0102 inches, and for the length of the Royal 

 Society's yard 36-0075 inches. The Parliamentary Committee 

 of I7S8 probably assumed the standard to consist of the rod and 

 matrix together, which seems the better view ; and by laying the 

 rod in its matrix, and measuring to the joint between them, Bird 

 would have got a length of about 36-0051 inches. The mean 

 between that and 36-0075 would be 36-0063, which differs very 



