3,^0 Comparifon of the Dejitiitive Mitre 



nlfli materials for a ninv map of Great Britain, were under- 

 taken, about 25 years ago, in England, and have been caT- 

 ried on fince that time. 'J'hefe labours, begun by the late 

 g^cneral Roy, have been condiifted with a great deal of fa- 

 gacity and precifion, and the refults of ihcni may atlovd in- 

 terefting data in regard to the figure of the earth. A diltin- 

 guilhed member of the Roxa! Socictv of London, Sir George 

 Schuckhurgh, has emplovcd himfelf, with fuccefs, in re- 

 fearches calculated to eftablilh the precife length of the 

 Itandards, which have ferved as a bafis to all the geodefian 

 incafurcnients made in Kngland. 



It was therefore {o be regretted that labour? fo analogous 

 In their nature, c.arried on in two neighbouring countries, and 

 fufeeptible ot acquiring, by eomparilon, a new degree of in- 

 tcreft, fliould reijiaia unconnected for want of a real li^mdard 

 of the meafures of one of thefe countries, viz. England. We 

 exjierieuced this regret in a very bvjely manner at diijfcreni; 

 periiods; and we eqii) vvjth truth allert, "that if the hope of 

 procuring this mean of companion was not ihc only motive 

 of the journey undertaken by one of us to England, it was a 

 firong iudue.enient i,()uards it. 



pur colleague, profclibr Pi(£hct, when he arrived at Paris, 

 togk fome fiej)^ to obtain airi authentic metre, in order th^t 

 he might fuboiit it to examination before the Royal Society 

 of London, of which he is a member; but, in confequence 

 of the fliortncfs of his flay in Paris, thefe fieps were not at- 

 tend-ed with tlie defirexl elled. |de, however, took advantage 

 pf vL longer ].eiidien|Le in England to procure i'rom Troughton, 

 311 artid celebrated for his accuracy in conlhutting '4].\4 di- 

 viding geometrical and atironomical iufirnmcnts, a ftandard 

 .exactly iimilar to one he had conrtrucled for Sir George 

 Seluickburgh, and to which that philofophcr referred the 

 principal Englilh meafurts in the memoir above meritiojied. 

 Our colleague alio caufcd 10 be conltruded by the fame 

 grtirt the comparative ajijiaratus of Sir George Shuckburgh, 

 confilling of two excellent microfcopes, one of which i-s fur- 

 Tiiihed with a micrometer that divides tlie Englifh inch into 

 ten tJ)oufand equal parts. (;n his return to'i'aris he took 

 the carlieil; (;)iporlunity of laving thele articles before the 

 Minifler of the Interior and the National Iiiftitute. I'his 

 Icarncil body named three of its members to proceed to a 

 Regular comparifon of tlie deliuitive nietre with the Randard 

 jul't mentioned. This labour, of a limiiler nature than it 

 might at firit appear, emplovcd the counniffioners during five 

 littnigs of four hours each, and wa< conducted with all tli^ 

 care "and attention that thcnaLuie of the objec'-t. required. 



C. Prony, 



