SURVEY OF MASSACHUSETTSS. 39 
there by sewing the bag firmly to them. ‘Their distance apart should be from a half to 
three-fourths of a yard. The cloth thus prepared is firmly secured to the upper end of 
the signal staff, by puckering the ends of the bag, and sewing them to it with strong 
twine; taking care so to arrange the ends as to cause them to support the signal bulb or 
balloon concentrically with the signal staff. We have sometimes bored a hole into the 
top of the signal staffand inserted therein a tuft of pine or other dark-coloured boughs,— 
a dark-coloured signal being frequently more conspicuous than a light-coloured one. 
The materials which compose the signal frame are frequently procured from the near- 
est forest trees; and are put together without any other dressing or preparation than 
merely depriving them of their branches, and fashioning their ends in a suitable manner 
to unite them into a firm and compact frame or tripod. ‘The frame is secured by passing 
through the upper end of the braces and through a point near the middle of the signal staff 
a strong wooden pin or an iron bolt. The whole will be sufficiently apparent from an 
inspection of the figures, without further description. 'The signal thus described, so far 
as my experience goes, has been found to answer well in all situations. It is readily 
and easily adjusted upon bare smooth rocks,—that is, as bare and as smooth as they are ever 
found in their natural position. I have placed them in soft swampy lands, and have found 
them to stand in those situations a long time without any perceptible derangement. 
4 Fig. 2. Fig. 2. represents a signal erected, and in suitable adjustment to be ob- 
_ served from other stations for the purpose of measuring angles therewith. 
I would here state that, as by far the greater portion of the primitive 
trigonometrical stations in Massachusetts are situated upon the tops of 
hills and mountains whose summits are bare rocks, or rocks very slightly 
covered, here and there, with earth, we have marked these points by drill- 
ing a small hole about two inches deep into the rocks, and inserting there- 
in a small copper bolt marked thus, @; and after having put our signal frame together, 
with the aid of a small tackle,—a derrick staff (as it is called in the language of seamen) 
secured in its vertical position with guy ropes or stays,—the signal is readily erected 
over the bolt, and that part of the signal staff which extends upwards from the meeting 
of the braces adjusted perpendicularly over the centre of the bolt. For determining 
when the signal was in proper adjustment, we used two small telescopes mounted very 
similarly to a transit telescope. These instruments, when placed in such a manner that 
the vertical planes of their motion, when passing through the centre of the upper bolt, 
would intersect each other nearly at right angles, would readily show, when pointed to 
any part of the signal staff, whether it was or was not in proper adjustment. By a move- 
ment of the lower ends of the braces, which is very easily performed, the whole of the sig- 
nal frame can be moved in any direction desired. Having put the main body of the sig- 
nal frame in its proper situation, the upper end of the signal staff may be rendered plumb 
by moving the lower end in an opposite direction. ‘The lower end of the signal staff 
comes very near the ground, but should not be allowed to touch it, and when it has ob- 
tained its proper place, the lower end is secured, and that of course secures also the up- 
per end, by piling a heap of small stones about it, if they can be found near at hand; or, 
when they cannot, by throwing about it a small mound of earth. Many signals of the kind 
described, which I erected at the commencement of the survey, were standing two years 
