BEAVER DAMS. 125 



measured in a straiglit line, when stationed at a dis- 

 tance of sixty-two feet, and show its structure with 

 sufficient minuteness, we adopted a plan to photograph 

 it upon seven such plates. In the first place, eight 

 stations were established, and flag-staffs erected, de- 

 fining the space assigned to each plate. Of these, the 

 first six were in a straight line, and each was in, or 

 near the crest line of the dam. At the sixth station 

 the general direction of the dam inclined down stream, 

 with which divergence the last two were made to cor- 

 respond. We then cut a line ten feet wide through 

 the thickets of willow and alder, removing the forest 

 trees as well, running it parallel with the flag-staffs, 

 and sixty-two feet below them. This line was for the 

 movement as well as to afford a position for the scaf- 

 fold for the instrument. After this, it was necessary 

 to determine the position for the scaffold in front of 

 each section of fifty feet of the dam, and then to cut 

 out a triangular opening between the two, having its 

 apex at the scaffold station. It was further found 

 advisable to make the first section of the dam, com- 

 mencing at the end on the right, seventy feet long, 

 the second, third, fourth, fifth, and sixth, each fifty 

 feet; and the seventh and last, seventy feet. The 

 first plate taken was to be of the second section, with 

 the scaffold immediately in front of its centre, and the 

 second of the first section, by turning the instrument 

 to the right, and not otherwise changing its position. 

 At this angle it would embrace the whole seventy 

 feet, as well as make the background harmonious as 

 to these two plates. After that the scaffold was to be 

 removed successively to the centre of each remaining 

 section on to the sixth, from which point the last sec- 



