Page:Proceedings of the Royal Society of London Vol 69.djvu/152

144 been good enough to furnish us with much valuable information, for which our best thanks are due.

The instrument chiefly employed was a 6-inch 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, l>. Station a was at a distance of 61 feet to the south-west of the centre of the temple, and I 364 feet to the north-east. The distance from the centre of Stone- henge to Salisbury Spire being 41,981 feet, the calculated corrections for parallax at the points of observation with reference to Salisbury Spire are :

Station + 4' 12". I -25 20.

(1.) Relative Azimuth*. Theodolite at station a

Salisbury Spire 000

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.) Absulitfe Azimuth*. All the azimuths were referred to that of Salisbury Spire, the azimuth of which was determined by observations of the Sun and Polaris.

(".) Observation of Sun, June 23, 1901, 3.303.40 P.M.

Mean of observed altitudes of Sun 41 26' 35"

Refraction

Parallax .. +

r4 "\ 58 6 J

True altitude of Sun's centre ...... 41 25 37

Latitude = 51 10' 42". Sun's declination - 23 26' 43". Usin the formula

sne. sn#

where A = azimuth from south, A = polar distance, c = co-latitude, and z = zenith distance,