APPENDIX 1
DETAILS OF THE THEODOLITE
OBSERVATIONS AT STONEHENGE
THE instrument chiefly employed was a
sixinch transit theodolite by Cooke
with verniers reading to 20" in altitude
and azimuth. Most of the observations
were made at two points very near the
axis, which may be designated by a, b.
Station a was at a distance of 61 feet
to the southwest of the centre of the
temple, and b 364 feet to the
northeast. The distance from the centre
of Stonehenge to Salisbury Spire being
41,981 feet, the calculated corrections
for parallax at the points of
observation with reference to Salisbury
Spire are:—
Station a + 4´ 12".
Station b  25´
20".
(1) Relative Azimuths.—Theodolite at
station a—
Salisbury Spire 
0° 0´ 0" 
N. side of opening in N.E.
trilithon of the external
ring 
237°
27´
40" 
Tree in middle of clump on
Sidbury Hill 
237°
40´
20" 
Highest point of Friar's
Heel 
239°
47´
25" 
S. side of opening in N.E.
trilithon 
240°
14´
40" 
Middle of opening in N.E.
trilithon 
238°
51´
10" 
(2) Absolute Azimuths.—All the azimuths
were referred to that of Salisbury
Spire, the azimuth of which was
determined by observations of the Sun
and Polaris.
(a) Observation of Sun, June 23, 1901,
3.303.40 P.M.
Latitude = 51° 10´ 42". Sun's
declination = 23° 26´ 43". Using the
formula
where A = azimuth from south,
Δ = polar
distance, c = colatitude, and z =
zenith distance,
we get
(b) Observations of Polaris.—June 23,
1901. Time of greatest easterly
elongation, calculated by formula cos
h=
tan φ cot δ, is G.M.T. 1.34 A.M.
Azimuth at greatest easterly elongation,
calculated by the formula
sin A = cos δ sec
φ,
is 181° 57´ 0" from south.
The mean of the two determinations gives
for the azimuth of Salisbury Spire S. 9°
8´ 2" E. This result agrees, well with
the value of the azimuth communicated by
the Ordnance Survey Office, namely, 9°
4´ 8" from the centre of the circle,
which being corrected by + 4´ 12" for
the position of station a, is increased
to 9° 8´ 20".
Hence, from the point of observation a,
9° 3´ 20" has been adopted as the
azimuth of Salisbury Spire.
We thus get the following absolute
values of the principal azimuths from
the point a :
The difference of 8˝´ between this and
the assumed axis 49° 34´ 18" is so
slight that considering the indirect
method which has necessarily been
employed in determining the axis of the
temple from the position of the leaning
stone, and the want of verticality,
parallelism and straightness of the
inner surfaces of the opening in the
N.E. trilithon, we are justified in
adopting the azimuth of the avenue as
that of the temple.
Next, with regard to the determination
of the azimuth of the avenue as
indicated by the line of pegs to which
reference is made on p. 65. The small
angle between the nearest pegs A and B
(which are supposed to be parallel to
the axis of the avenue), observed from
station a, was measured, and the
corresponding calculated correction was
applied to the ascertained true bearing
of the more distant peg B.
Thus
The mean of the three independent
determinations by another observer was
49° 39´ 6".
The calculated bearing of the more
distant part of the axis of the avenue
determined in the same manner by
observations from station b is 49° 32´
54". The mean of the two, namely, 49°
35´ 51", justifies the adoption of the
value 49° 34´ 18" as given by the
Ordnance Survey for the straight line
from Stonehenge to Sidbury Hill.
(3) Observation of Sunrise.—On the
morning of June 25, 1901, sunrise was
observed from station a, and a setting
made as nearly as possible on the middle
of the visible segment as soon as could
be done after the Sun appeared.
The telescope was then set on the
highest point of the Friar's Heel, and
the latter was found to be 8´ 40" south
of the Sun.
The observation thus agrees with
calculation, if we suppose, about 2´ of
the Sun's limb to have been above the
horizon when it was made, and therefore
substantially confirms the azimuth above
given of the Friar's Heel and generally
the data adopted.
