﻿222 MAGNETIC OBSERVATIONS ON THE MEXICAN BOUNDARY LINE. 



vation and station errors ; nor is the value of the mean result affected thereby, which 

 forms a valuable datum in absolute measure, in an almost inaccessible region of the 

 globe. 



In order to compare this measure of force with that previously obtained on the 

 northern line by observations with a Fox apparatus, and expressed in the arbitrary 

 scale, we may have recourse to the observations of Captain Lefroy at Toronto, which 

 gives the total force in British units = 13.86 at the same time that it is found 1.836 

 in the arbitrary scale. Applying the same ratio to our mean total intensity, 11.65, we 

 find 1.543, and we have the following comparison : — 



Latitade. Longitttde. Total Intensity. 



31 27 108 4o 1.543 



32 43 108 30 1.580 



the latter from three stations in 1851; exhibiting a closer correspondence than might 

 be expected from the circuitous comparison involved. 



