jVA ture 



[Jamuary 7, 1909 



position \kg, crossing tlie plane of^ the ecliptic in g, 

 tlie earth's axis will occupy the position Qp' . 



The lines Cp rnd C^' have both the same inclina- 

 tion to CQ. It follows, therefore, that the motion of 

 the earth's axis due to precession consists in a slow 

 revolution round the axis of the celestial sphere, per- 



FlG. 26.— General Pla 



ihe outer circle, 



pendicular to the plane of the ecliptic. During this 

 movement, while the inclination of the two planes 

 remains nearly 235°, the position of the celestial 

 pole, and consequently our ]jole star, are constant!) 

 changing. 



Fig. 27. — Showing the effects of p 



the position of the 



'I'he precessional globe, as I called it, is, in fact, 

 arranged so that the position of the celestial pole aiil 

 equator, and consequently the positioiis of the st;irs, 

 may be represented at any epoch. In the globe ])ivols 

 are provided so that it may be turned on the ])i)l(' of 

 the ecliptic ; round these at a radius of 233° are brass 

 circles (one of which is shown), with holes 

 in them, each of which may also be used 

 as a pivot. One pair of pivots on the 

 latter circles corresponds to the present 

 celestial uoles, and represents the heavens 

 as thev are at the present time ; the globe 

 is arranged to turn on these, the ecliptii 

 pivots being thrown out of gear. Other 

 pivo:s on the brass circles correspond to 

 o;her dates, the whole circle being tra- 

 about 25,800 years. For example, if we wish 

 globe to represent the conditions 2000 years 

 first swing the globe 0:1 the poles of the 

 hen turn it until the desired jjoints on the 

 le are brought under the other pivots. Thes j 

 screwed into position, and the first two ai j 



s a brass meridian, passing round the globe 



ngles to the hori/on, which is graduated as 



inary celestial globe. 



astronomers, including the late Mr. Hind. 



kworth. Dr. Lockyer, and Mr. Stockwell, 

 upied themselves in calculating the rigln 

 s and declin.-itions occtipird b\ vinr-- in p.'ist 



An ordinary celestial globe represents the right 

 ascensions and declinations of stars at some epoch near 

 our own time, but some years ago I devised a globe 

 in which the changes brought about by this preces- 

 sional movement can be shown in a very concrete 

 manner, so that the changes in position can be readily 

 understood. 



NO. 2045, VOL. 79] 



Kic. 28.— The Precessional Globe. A, Poleol ecljpii.: ; ri, hrass circle, with 

 holes on positions of celestial poles at dilTerent epochs; c, screw pivot 

 for N. pole of ecliptic ; D, screw pivo: for N. celestial pole at different 

 epochs ; E, scale of years denoting position of celestial pole at definite 

 epochs (set for 1364 B.C.); F-n, brass meridian; H, H, H, H, wooden 

 horizon ; J, ecliptic ; k, celestial equttors drawn for different epochs. 



times. Curves given in " Stonehenge " (pp. 116-117) 

 show the changing declination of the brightest stars — 

 and this is the component of greatest importance to 

 the archsologist — from 250 .\.D. to 2150 B.C. 



