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 „ „ „ 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_, 3.30-3.40 P.M. Mean of observed altitudes of Sun 41° 26′ 35″ Refraction -1′ 4″} 0 0 58 Parallax + 6 } ----------- True altitude of Sun’s centre 41 25 37 Latitude = 51° 10′ 42″. Sun’s declination = 23° 26′ 43″. Using the formula sin ¹⁄₂(Δ + _c_ - _z_) sin ¹⁄₂(Δ + _z_ - _c_) cos² ¹⁄₂ A = -------------------------------------------- sin _c_ . sin _z_ where A = azimuth from south, Δ = polar distance, _c_ = co-latitude, and _z_ = zenith distance, we get Azimuth of Sun S. 75° 30′ 30″ W. Mean circle reading on Sun 84 38 35 ---------- Azimuth of Salisbury Spire S. 9 8 5 E. (_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. Observed maximum reading of circle 256° 33′ 0″ True azimuth of star 181 57 0 ---------- Meridian (S.) reading of circle 74 36 0 Circle reading on Salisbury Spire 65 28 0 --------- Azimuth of Salisbury Spire S. 9 8 0 E. 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° 8′ 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_: