Page:Proceedings of the Royal Society of London Vol 69.djvu/154

146 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 in the body of the paper. 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 calcu- lated correction was applied to the ascertained true bearing of the more distant peg B.

Thus

True bearing of peg B = 238 35' 0"

Calculated correction to peg A = 12 8

True bearing of line AB 238 47 8

Bearing of Salisbury Spire 189 8 20

True bearing of a line parallel to the axis of near part of avenue N. 49 38 48 E.

The moan 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 I 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, sun- rise 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, nnd the latter was found to lie 8' 40" south of the Sun.

Sun's declination at time of observation... 23 25' 5" Elevation of horizon at point of sunrise ... 35 48 Assuming 2' vertical of Sun to have been visible at observation, we have ap- parent altitude of Sun's upper limb 37 48

Refraction -27' 27" "1 _^ ^ -.Q

Parallax ..+ 9 J

True altitude of upper limb 10 30

Sun's semi-diameter. 15 46

True altitude of Sun's centre. -0 5 16