The Journal of the Astronomical Society of India. March 1913

The President also by a diagram on the black-board showed the distinction between the Celestial Pole the Pole of the Ecliptic and the Galactic Pole. [...] The above is the test by means of examination of the whole surface of the mirror from the centre of curvature of the ouside zone. [...] I have referred above to the method of finding the centre of curvature of the zones of the mirror separately by using suitable discs to cover the portions of the mirror not actually under test and I showed that the centres of the successive zones in the case of a spherical mirror would be at the same point. [...] They would be so if the axis of the earth was rigidly inclined to any partcular point in the heavens but in consequence of the moon's attraction on the redundant matter at the earth's equator the axis of the earth undergoes a slow gyratory motion which is called nutation similar to that of a peg top when spinning and this motion has the effect of causing the pole in the heavens to describe [...] The temperature of the sun the intensitdifference of the spectrum of which forms the basis of the calculations is on this scale 4950°.