. 
to break them ys 
rr 
‘ 
On the Measurement of a Base on Epping Plains. 59 
Sub-assistant J. A. Sullivan and Mr. Webber, and the profile 
was studied upon a sketch of the plain made by Lieut. Clark. 
In 1856 I examined the site, and took steps to obtain the 
necessary estimates of the cost of preparing it for measurement. 
The profile of the line as graded gives a good general idea of 
= — as it varied but little from the natural profile. (See 
tc 
etch. 
The whole length of the line is about 8719 meters or 5°4 
miles. Its general direction is E. 16° S. (true bearing.) 
From the eastern end for about four miles the plain is quite 
level, rising in the first mile pretty regularly about fifteen feet, 
escending nearly as much in the next to rise by the same quan- 
¥ in the third mile. It then runs along an elevated level for 
aiourth of a mile and descends gradually to the rougher part of 
the base which is included between the 3% miles from the east 
end and the western end of the base. 
This line was skillfully graded by Mr. Boutelle, so as to follow 
the natural surface when the grade did not run above three de- 
grees, and to give as long slopes as possible of the same grade 
for the convenience of measuring. (See sketch.) 
As it was found more economical to make the temporary 
embankments than to excavate, a profile giving a considerable 
excess of embankment was selecte ; 
_This was executed in the cheapest way which would give sta- 
bility for the time during which it was required to stand. The 
east width was twelve feet, of which nine feet was on the south 
and three feet on the north side of the line to be measured. Th 
was very carefully aligned. High signals were placed over 
the termini which are inter-visible. On the Schoodiac a signal 
of moderate elevation is visible from both, and the distances be- 
tween this point and the termini were gradually subdivided, 
until the smallest limit, the distance easily reached by a small 
transit, was obtained. : , : 
he verification of the alignment at different points of the 
Measurement when the seeing was good was complete. 
Tn all these preliminary operations Mr. Boutelle was assisted 
by Sub-assistant J. A. Sullivan and Mr. Webber. 
iS grading partly consisted of the farmers and lumbermen of 
the district who served with great cheerfulness and skill in the 
use of the heavy implements for rough grading. One of the 
Sreatest difficulties was the removal of such boulders as were in 
the line, many of them being of such size as to require blasting 
: , and some being actually removed to the re- 
quired distance from the line by heavy blasts. 
The signals erected at the two ends are very substantial, each 
forty-three feet in height to the top of the tripod and fifty-three 
%© the cone which surmounts them. 
