Himautava Mountains, 283 
even or free from a slight bend downward: yet when the tension is sreat, 
and the weight of the string little, its deviation from the line joining its two 
extremities, may be so small, as to be inappreciable by sense. The brass 
wires already mentioned were thin, and they were stretched by a weight a 
little short of the maximum, they were capable of bearing. ‘They may 
therefore be supposed to have been rectilineal.* The small bridges alrea- 
dy noticed being of the same height as the wire at its extremities, and the 
groove allowing of the wires being depressed m the case of the rod lying: 
uneven, it was seen immediately by the’ position of the wire, whether the 
rods were situated in the intersection of the hypothenusal and vertical 
planes, and if not they were easily brought into the required: position by 
means of the small wedges already noticed, applied under and on either 
side ofthem. Perhaps it will be said, that this method was troublesome 
and consumed time; no doubt it did: but certainly not so much, as the em- 
ployment of trussed rods and stands with elevating screws would have 
done—and indeed when my people began fairly to understand what was 
meant, I got through the work quick, and found om passing along the line 
of rods hardly ever cause to touch the adjustment myself. Fig: 6, repre- 
sents this contrivance on a large scale. 
IJ. Ir has been already noticed how small the error of pine rods was 
found by General Roy. His method however of comparing the rods, 
several times during the day, with a standard, was in some measure 
* Axcrnovucu the truth-of this be evident, and that it was confirmed by experience, yet it may be well 
to notice here, that supposing the wire to have fallen in the middle, below the straight line 4 of an inch, 
which it certainly did not, the error in the length of the rod would be only 455 of an-iach, 
