Lynn pointed out, 13 to refer to the time when a Draconis ' Lenormant, Origines, i.
36, 49 in the Laurentian library) had a gap at the beginning of the line and only the end words "uetus est tutela draconis," with the marginal note "non potuit legi in exemplari hoc quod deficit," and that Neap. 268 gives the line as follows, "non potuit legi uetus est tutela draconis."
Hooke, in 1674, published his observations of y Draconis, a star of the second magnitude which passes practically overhead in the latitude of London, and whose observations are therefore singularly free from the complex corrections due to astronomical refraction, and concluded that this star was 23" more northerly in July than in October.
They determined to reinvestigate the motion of y Draconis; the telescope, constructed by George Graham (1675-1751), a celebrated instrument-maker, was affixed to a vertical chimneystack, in such manner as to permit a small oscillation of the eyepiece, the amount of which, i.e.
The instrument was set up in November 1725, and observations on y Draconis were made on the 3rd, 5th, 11th, and 12th of December.
One hypothesis was: while y Draconis was stationary, the plumb-line, from which the angular measurements were made, varied; this would follow if the axis of the earth varied.
Nutation of the axis would determine a similar apparent motion for all stars: thus, all stars having the same polar distance as y Draconis should exhibit the same apparent motion after or before this star by a constant interval.
Many stars satisfy the condition of equality of polar distance with that of y Draconis, but few were bright enough to be observed in Molyneux's telescope.
One such star, however, with a right ascension nearly equal to that of -y Draconis, but in the opposite sense, was selected and kept under observation.
This star was seen to possess an apparent motion similar to that which would be a consequence of the nutation of the earth's axis; but since its declination varied only one half as much as in the case of y Draconis, it was obvious that nutation did not supply the requisite solution.