still better shown with a Saturnian orrery (see plate viii. of my Saturn), which can be very easily constructed. [31] Not 'of course' because Tycho used it, for, like other able students of science, he made mistakes from time to time. Thus he argued that the earth cannot rotate on her axis, because if she did bodies raised above her surface would be left behind--an argument which even the mechanical knowledge of his own time should have sufficed to invalidate, though it is still used from time to time by paradoxers of our own day. [32] Chinese chronicles contain other references to new stars. The annals of Ma-touan-lin, which contain the official records of remarkable appearances in the heavens, include some phenomena which manifestly belong to this class. Thus they record that in the year 173 a star appeared between the stars which mark the hind feet of the Centaur. This star remained visible from December in that year until July in the next (about the same time as Tycho Brahe's and Kepler's new stars, presently to be described). Another star, assigned by these annals to the year 1011, seems to be the same as a star referred to by Hepidannus as appearing A.D. 1012. It was of extraordinary brilliancy, and remained visible in the southern part of the heavens during three months. The annals of Ma-touan-lin assign to it a position low down in Sagittarius. [33] Still a circumstance must be mentioned which tends to show that the star may have been visible a few hours earlier than Dr. Schmidt supposed. Mr. M. Walter, surgeon of the 4th regiment, then stationed in North India, wrote (oddly enough, on May 12, 1867, the first anniversary of Mr. Birmingham's discovery) as follows to Mr. Stone:--'I am certain that this same conflagration was distinctly perceptible here at least six hours earlier. My knowledge of the fact came about in this wise. The night of the 12th of May last year was exceedingly sultry, and about eight o'clock on that evening I got up from the tea-table and rushed into my garden to seek a cooler atmosphere. As my door opens towards the east, the first object that met my view was the Northern Crown. My attention was at once arrested by the sight of a strange star outside the crown' (that is, outside the circlet of stars forming the diadem, not outside the constellation itself). The new star 'was then certainly quite as bright--I rather thought more so--as its neighbour Alphecca,' the chief gem of the crown. 'I was so much struck with its appearance, that I exclaimed to those indoors, "Why, here is a new comet!'" He made a diagram of the constellation, showing the place of the new star correctly. Unfortunately, Mr. Walter does not state why he is so confident, a year after the event, that it was on the 12th of May, and not on the 13th, that he noticed the new star. If he fixed the date only by the star's appearance as a second-magnitude star, his letter proves nothing; for we know that on the 13th it was still shining as brightly