WILSON ON GEOGRAPHICAL WORK OF THE SURVEY. 711 



there may sometimes be reasons why one point is more liable to error 

 than the others, and in that case another column may be selected if its 

 sum difters but little from the smaller sum ; as a rule, it is best always 

 to choose the column that gives the least aggregate swing. These cor- 

 rections, both fore and back, should be recorded immediately in some 

 convenient form, as they are taken to account in all subsequent triangles 

 in which these sides enter. In this manner the work is carried on from 

 station to station until all are located. 



The method of plotting the results as calculated from the uncorrected 

 foresights I consider a very good check on the previous work, as any 

 erroneous location in the previous work must appear at the new point 



Figure 4, Plate 35, represents the foresight intersections as plotted 

 from the preliminary calculations for the location of Mount Rito Alto 

 All of these sights come within a circle of about 5 feet diameter, the 

 center of which is assumed to be the most probable position, and the 

 sights were accordingly swung to that point. 



Figure 5 represents the condition of the foresight intersections on 

 Summit Peak. Here we have one of the widest ranges occurring in the 

 calculations of the work of 1876, and this is probably due to this point 

 presenting a broad top as seen from the northeast, and all of the sights 

 from that direction are taken from a long distance ; but as four out of 

 the eight sights used meet very nearly, those triangles sum np very 

 close to 180°, while the triangles containing the sights from Mount Rito 

 Alto, Hunt's, Stations 24 and 28, sum up too large. 1 assumed the 

 error to be mostly on those sights, and was convinced that the intersec- 

 tions of the sights from Blanca and South River Peaks are correct, ac- 

 cordingly swung the other sights to that point. 



Figure 6 represents the sights as plotted on Rio Grande Pyramid, and 

 the small triangle the point chosen as the station. Figure 3 shows the 

 condition of sights on West Elk Peak. 



Figure 2 gives the intersections on Mount Wilson. The peculiar posi- 

 tion of this point makes it one of the best proofs of the accuracy of the 

 previous work that occurs in the whole system, although it was only oc- 

 cupied as a secondary station. But it was sighted from every direction, 

 and the various points from which it was sighted were more or less located 

 by a different series of triangles. The arrow-point shows from which di- 

 rection the sight was taken, and the name of the point from which it was 

 taken is placed on the other end of the line, or, in other words, nearest 

 the station. All of these sights meet within a small area except one, 

 and that being so much out as compared with the others, it is probable 

 that some error was made in sighting from that station ; therefore it was 

 given no weight in the final location of the point. Many more exam- 

 ples might be given, but these few will be suiTicient to give an idea of 

 the character of the work, and will also serve to illustrate the general 

 method of adjustment. 



I consider the foregoing method of adjustment very simple, and, at 



