§52 SURVEY OF THE COAST 



scale is far less satisfactory than the successive mechanical 

 addition of a number of copies made from a standard unit, 

 and compared to the same, or any other, by proper means. 

 'J'his conviction, derived from experience and a careful com- 

 parison of the modes of proceeding used in tlie late works 

 of this nature in Europe, decided me to adopt, for the unit 

 measure of the bars intended for \he base, the combination 

 of four iron bars, each of two metres in length. 



I had one more decisive reason for tliis choice, viz. that I 

 had at my disposition one of the metres standarded by the 

 Committee of Weights and Measures in Paris, in 1799, which 

 being of the same authenticity, in all respects, witli any of 

 these measures in the possession of the respective govern- 

 ments, and with the platina metre of Paris, places the ac- 

 curacy of my unit measure beyond all possible doubt. The 

 comparison made between the different standards, this being 

 among the number, reduces any multiple length of my de- 

 terminations to any standard desired, ijy an easy numerical 

 calculation. 



This comparison of the different standards, and the stand- 

 ardingof tlie bars for the baseline, I executed in the months 

 of February and March, 1817; but I intended to repeat all the 

 comparisons again, before the measurement of tlie first base 

 line with the bars. I had likewise intended to compare the 

 standard metrical and troy weights, of which I had a full and 

 authentic collection, by the fine balances placed in the col- 

 lection for that purpose, and by anotlier founded on hydro- 

 static principles, invented by my friend and teacher, M. 

 Tralles. All these it was not possible for me to effect: I 

 will however here record what I have been able to do in this 

 respect. 



I will first give an account of the particular standards 

 which I have compared, and of their origin, so that a judg- 

 ment may be formed of their authenticity. I shall also state 

 the means employed in their comparison, and for the stand- 

 arding of my bars, — to shew the degree of reliance which 

 may be placed in my results. 



