OF THE UNITEn STATES. 351 



tlifTercnt metals, whicli circumstance has always presented 

 ditriculties ii] tlieir comparison. 



The Knglish standard is a hraas scale, divided into inches 

 and tenihs of inches. U|)on this, the mean of all the possi- 

 ble n>easiircments of any distance is considered as the pro- 

 per standard value of that distance, the yard and the foot 

 measured in this manner heins; equally lei!;al standards, 

 thou2;h prol)al)ly the yard was originally intemled as such. 

 The diffVrent scales are of ditlerent aa;es and accuiacy ; hav- 

 ing been successively improved by various artists, by mak- 

 ing scales from the mean lengths of various distances, taken 

 according to convenience, upon the scale from which the 

 new standard was co|)ied. Upon this siilyect. Sir George 

 Simcki)urgh Evclin's Account of tlie Comparison of Mea- 

 sures may be consulted. — Philosophical Transactions of Lon- 

 don, 1798. 



'I'he Fi'ench standard consists in a certain determined unit 

 of length in iron, given by a bar cut off' to the given length, 

 either a toise, as formerly, or, as at present, a njetre ; the 

 iron toises of Peiu being the only authentic original to 

 which all toises are referred, and the metres of the Commit- 

 tee of Weights and Measures the authentic originals of the 

 metres. Of their ratio and the mutual comparison of their 

 measures, the '• Base du Systeme Metrique" gives a suffi- 

 cient account. 



The standard temperature of the V^nglish scale is 63° 

 of Fahrenheit's thermometer ; that of the French metre 33° 

 of the same scale; and the metre having been compared 

 with the toise at this temperature, it ha-* also been adopted 

 for the toise, which was formerly referred to J0° of llcau- 

 mur's scale. 



He who has ever attempted to copy any al)soliitc mea- 

 sured length, with the accuracy necessary to form a standard, 

 must have soon discoveied what great minuteness, and care 

 in the choice of means, an- retpiired for this |)urpose. 

 Beam compasses and similar fiicans will soon be I'ou'hI in- 

 admissible. 'J'he successive transfer of a measure from a 



