ALTAZIMUTH SOLAR OBSERVATIONS. 309 
Tut RIGOROUS THEORY or tar DETERMINATION or 
THE MERIDIAN LINE sy ALTAZIMUTH 
SOLAR OBSERVATIONS. 
By G. H. Kyreps, r.n.4.s., Lecturer in Surveying, University of 
Sydney. 
[Read before the Royal Society of N. S. Wales, December 2, 1896.] 
Introduction. 
Instrumental theory. 
Almucantars and great circles tangent thereto. : 
Error of the mean of true altitudes as a datum for the computation 
of azimuth or time: zero declination. 
- Ditto: any declination. 
- Refraction error of the mean of observed altitudes. 
99 to 
. Augmentation of the Sun’s semidiameter. 
- Contraction of the Sun’s horizontal semidiamer by refraction. 
- Contraction of the Sun’s vertical diameter by refraction. 
- Elliptical figure of the Sun’s image. . 
- Contraction of inclined semidiameters and departure from elliptical 
form 
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- Elliptical image of the Sun, tangent to two diaphragm wires inclined 
at any angle. 
15. Ditto, tangent to perpendicular and horizontal diaphragm wires. 
“4 Elliptical image of the Sun tangent to one diaphragm wire. 
21. Conditions of precision and general remarks. 
1. Introduction.—Although it cannot be expected that solar 
observations for the determination of the meridian line, will yield 
results equal in precision to those which may be derived from 
Stellar observations—chiefly on account of the greater unsteadiness 
of the atmosphere during the day, and of the larger uncertainty 
in the magnitude of the refraction—yet their convenience often 
