7i6 



NATURE 



[February 25, 1915 



fallen off the slipping is the other way and a couple 

 which produces the reverse effect results, and the top 

 falls. 



[Experiments were here made with a gyrostat on 

 gimbals, and with a gyrostat mounted on a trapeze 

 hung by the crossed cords of a bifilar suspension. 

 See "Gyrostats and Gyrostatic Action," Nature, 

 April 10, 19 1 3, to illustrate the stabilising by spin of 

 a gyrostat with two freedoms, both unstable without 

 spin.] 



As I have already stated, Lord Kelvin illustrated, 

 by what he called a "liquid gyrostat," the fact that 

 an oblate spheroidal shell filled with water behaves 

 as regards precession as if its contents were solid. 

 Here is the gyrostat with which the experiment was 

 made (Fig. 8). It resembles the ordinary gyrostat, 

 but the case is not completely enclosed, and the 

 spheroidal globe containing water tal<es the place of 

 the flywheel : these are the only points of difference. 

 I spin the globe in the ordinary way, and you see 

 that in all respects the liquid gyrostat imitates the 

 behaviour of the solid one. 



instability of the motion, the energv of rotation has 

 been entirely transformed into heat, by turbulent 

 motion of the water, into which the rotational motion 

 breaks down. Permanent steady rotation of the 

 liquid globe is impossible. 



Oblateness, however, is not absolutely essential for 

 steady rotational motion of a liquid round the axis of 

 figure in a spheroidal case turning with the liquid. 

 It was shown by Sir George Greenhill in 1880 (three 

 years after the meeting of the British Association at 

 Glasgow) that steady motion is possible in a prolate 



Fig. 8. — Liquid Gyrostat (Oblate). 



This spheroid has an oblateness of about 5 per 

 cent. ; that is, the difference in length of the polar 

 and equatorial diameters is about 5 per cent, of the 

 length of either. Here, however, is another liquid 

 gyrostat which has about 5 per cent, of prolateness 

 (Fig. 9). I attempt to spin it, and you see that as 

 soon as it is removed from the spinning apparatus 

 its spin has entirely disappeared. In consequence of 



NO. 2365, VOL. 94] 



Fig. 9. — Liquid Gyrostat (ProlateX 



Spheroid, if it be sufficiently prolate. The axial 

 diameter, in fact, must either be shorter than the 

 equatorial diameter, or be more than three times as 

 long.^ As Sir George Greenhill points out, a modern 

 elongated projectile if filled with a liquid would not 

 rotate steadily about its axis of figure, and therefore 

 would not have a definite trajectory as a rifle bullet 

 has ; it would turn broadside on to the direction of 

 motion. 



(J^o he continued.) 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Bristol. — The Society of Merchant Venturers, in 

 whose Technical College the faculty of engineering 

 is provided and maintained, has decided to offer ten 

 scholarships, tenable in the faculty for three sessions, 

 beginning with the session 1915-16, to the sons of 

 officers in his Majesty's Service who have been killed 

 in the war, and whose mothers or guardians are in 

 needy circumstances. 



Cambridge. — The adjudicators of the Smith's prizes, 

 and the Rayleigh prizes are of opinion that the fol- 

 lowing essays sent in by the candidates are of dis- 

 tinction : — H. Glauert, of Trinity College, on the 

 elliptical form of a rotating fluid mass as disturbed by 

 a satellite, and H. Jeffreys, of St. John's College, on 

 (i) certain hypotheses as to the internal structure of 

 the earth and moon, (ii) on a possible distribution of 

 meteors, to whom the .Smith's prizes have been 

 awarded in alphabetical order. A Rayleigh prize has 

 been awarded to J. Proudman, of Trinity College, 

 for his papers on tidal motions. 



Mr. Herbert A. L. Fisher, vice-chancellor of the 

 University of Sheffield, has been elected a trustee 

 of the British Museum, in succession to the Right 

 Hon. Sir George O. Trevelyan, Bart., O.M., who 

 has resigned on account of ill-health. 



" Proceeling* of the Camhridge Philosophical Society, iS8o Encyclo- 

 pa:dia I ritannica," article, '" Hjdromechanic-.." 



