1887.] ^^1 [Taylor. 



that it ouglit to vibrate more rapidly toward tlie poles than toward tlie equa- 

 tor. He accordingly tried the pendulum at Uranibourg, at Paris and at 

 Cette, but wab not fortunate enough to discover any sensible difference. 

 Eoemer also found the length the same at London. 



Richer, however, in the same year, 1671, or early in 1672, wliile engaged in 

 the duties of his commission at Cayenne, on observing the length of the sec- 

 onds' pendulum at this place (lat. 4° 56' north of the equator), found it sen- 

 sibly shorter than at Paris (48° 50' north), the difference being about aline 

 and a quarter. Picher's discovery that the pendulum varied in length with 

 the latitude, deprived it of that uniform character considered so necessary in 

 a linear stdndard. 



The Abbe Gabriel Moiiton, a distinguished mathematician who flourished 

 at the same time, appears to be the first who suggested a measure derived 

 from the earth. He proposed, almost simultaneously with the publication of 

 Huyghens, a decimal system of measit res hKsed on the value of a minute of arc, 

 as derived from Piccioli's length of a degree. This minute of the degree he 

 called a miliare, the thousandth part of which he called a virrja, equal to 5 

 feet 4'^ inches. We have here the germ of the present French metrology. 



Cassini, who in 1718 repeated the measurements of a meridian made by 

 Picard (extending his arc, however, further south, namely, from Paris to 

 Dunkirk, and making the degree 69.119 miles), proposed the earth's radias 

 as the unit of length. He afterward in his book, " Be la Grandeur de la 

 Terre," proposed as a unit the six-thousandth part of a minute of a degree 

 of a great circle of the earth, a measure very nearly equal to the foot. 



In 1748 M. de la Condamine (who had recently returned from measuring a 

 degree at the equator in Peru), in a memoir read before the Academy of 

 Sciences, resumed the idea of the pendulum as the unit of length, proposing 

 that it should be taken as beating seconds at the equator, as the most notable 

 line of latitude, and as one likely to avoid all the prejudices which might arise 

 from national jealousy were the latitude of any particular place selected. 

 "We see from this the anxiety felt to secure a standard whicli might be com- 

 mon and uniform among nations. 



On the 15th of January, 1790, in accordance with President Washington's 

 recommendation, the House of Pepresentatives 



"Ordered, That it be referred to the Secretary of State to prepare and 

 report to this House, in like manner, a proper plan or plans for establishing 

 uniformity in the currency, weiglits and measures of the United States." 



On the 15th of July of that year the House of Representatives received 

 from the Secretary of State (Mr. Jefferson) his report of the proper plan for 

 establishing the desired uniformity, as requested by the House. 



In this elaborate report the Secretary proposed " that the standard of mea- 

 sure be a uniform, cylindrical rod of iron of such length as, in latitude 45°, 

 in the level of the ocean, and in a cellar or other place, the temperature of 

 which does not vary through the year, shall perform its vibrations in uniform 

 and equal arcs in one second of mean time." 



Starting from this standard, he proposes two distinct plans for the consid- 

 eration of the House, that they might, at their will, adopt the one or the 

 otlier exclusively, or the one for the present and the other for the future time, 

 when the public mind may be supposed to have become familiarized to it. 



The first plan was to define and render uniform and stable the existing sys- 



PROC. AMEB. PHILOS. SOC. XXIV. 136. 2t. PRINTED DEC. 2, 1887. 



