154 ' rRANSACTTONS iSqQ-'oO 



article of the Convention of 1818 as being the parallel of 49 

 degrees north latitude. The immediate cause of the delimitation 

 of the boundary was the discovery that the fort of the Hudson's 

 Bay Company at Pembina was nearly a mile within United States 

 territory. 



The field work was begun in September 1872 and finished in 

 the same month two j^ears later, while the proceedings of the 

 joint commission were brought to a conclusion May 29th, 1876. 



On this line of 860 miles, 40 astronomic stations were estab- 

 lished, and 388 monuments erected. 



After due consideration, the commissioners agreed upon the 

 astronomic parallel. The recommendation for this, by the chief 

 astronomers of the commission, was based on the following 

 grounds : "ist That the portion of the parallel of 49° included 

 within the operations of the commission, being only about one 

 twentieth of the entire circle of latitude, was not surFicient to fix, 

 with any mathematical accuracy, the true position of the mean 

 line of 49°, and that, therefore, if such a parallel were described, 

 depending on the mean of the astronomic stations, no known 

 point of the boundary would be in latitude 49° ; 2nd That as the 

 amplitude of the arcs, included between the mean and the astron- 

 omical parallels, would in many cases be very considerable, grave 

 errors and complications might arise in the subsequent re-survey 

 of any lost portion of the boundary ; 3rd That the definition of 

 a mean line would involve a re-adjustment of the whole boundary, 

 after the first careful survey should have been completed, and 

 consequently a very considerable increase of expense, without any 

 practical benefit accruing ; 4th That for every purpose except 

 that of geodetic computation, a parallel of points determined as- 

 tronomically (instrumental errors aside) , is a true parallel of 

 latitude, and therefore, fulfils the stipulations of the treaty under 

 which the joint commission was organized." 



Accordingl}^ , astronomic positions were determ.ined at ap- 

 proximate intervals of twenty' miles. These stations were con- 

 nected by tracing upon the ground tangents to the prime vertical 

 circles at each successive point. From these tangents, checked 

 and corrected for errors of azimuth, the calculated offsets to the 

 small circle of latitude were measured at convenient intervals. 



