588 SCIENCE PROGRESS 



however, that the pole of the heavens now at p (near P), instead 

 of keeping at a constant distance from the centre E, has been 

 decreasing its distance for 3,000 years at least, causing the 

 obliquity of the ecliptic, the tilt of the earth to its orbit, to 

 decrease continuously. The present angle is shown as 23 , 

 without the minutes and seconds. Drayson was determined 

 to find out the cause of the decrease on this reasoning : 



It might be possible, he thought, that the pole of the heavens 

 always moved round the pole of the ecliptic E as a focus, 

 but since these poles were known to decrease their distance 

 47*'6 per century, then the course of the pole could not be a 

 true circle. Also it might be possible that the course of the 

 pole was a true circle, but in this case the centre of the circle 

 could not be coincident with the pole of the ecliptic. 



After years of incessant labour, Drayson proved that the 

 course was a circle, of which the centre C was 6° removed from 

 the pole of the ecliptic E. Hence the circle described was 

 larger than had been imagined, and would require, to be com- 

 pleted, about 31,756 years and not 25,868 as has been stated by 

 astronomers. 



He was thus able to attribute the decrease to the simple 

 fact that the pole of the ecliptic is not the real centre, but 

 that PRP' centred on C is the true circle of the movement. 

 These two circles are here shown in perspective. This discovery 

 enabled him to state that the points P, E and C would be on 

 the same great circle of the sphere in the year a.d. 2295. 

 Tracing back from this date against the direction of the 

 arrow, he found that when the pole was at P' the obliquity 

 would be about 35|°, i.e. 12 greater than at present, the 

 obliquity being always measured by the distance between 

 the pole of the heavens and the pole of the ecliptic E. This 

 would cause a 50 per cent, increase in the tilt of the earth 

 to its orbit, which of course would increase the arctic circles 

 to the same amount, and consequently the extent of the ice- 

 caps to a corresponding degree, causing a glaciation of the 

 temperate regions in both hemispheres, bringing the arctic 

 circle in this country as far south as Durham. Its present 

 position is just north of Iceland. 



The curve of the Drayson cycle is represented in fig. 2, 

 taken from Draysonia (Longmans), by Admiral Sir Algernon 

 de Horsey, a book dealing with the astronomical aspect of 



