RECENT ADVANCES IN SCIENCE 4 37 



It is well known that when a comparison of the observations 

 of the Moon is made with theory, there are certain deviations 

 in longitude which remain unaccounted for. Prof. E. W. 

 Brown in an address to the British Association in 19 14 {Brit. 

 Assoc. Report, 1914) pointed out the similarity between the 

 deviations of the Moon and those of the Sun and Mercury. 

 H. Glauert,in two papers entitled " The Rotation of the Earth " 

 (M.N., R.A.S. vol. lxxv. pp. 489 and 685), discusses whether 

 such deviations are explicable by a small change in the rate 

 of rotation of the Earth. Since such a change would cause a 

 corresponding change in the unit of time, it would make itself 

 apparent as an error in position of any body moving fast enough 

 to show the effect. The result of the discussion is that the 

 errors in longitude of the Sun, Moon, Venus, and Mercury 

 can be accounted for by a slight and rather irregular change 

 in the Earth's rate of rotation, the increase in the length of 

 the day being about o - oi seconds in a third of a century : the 

 corresponding change of momentum may be entirely or par- 

 tially compensated by a change in the Moon's mean motion. 

 Sir Joseph Larmor (M.N., R.A .S. vol. lxxv., p. 2 1 1 ) has examined 

 the possible physical causes of such an irregularity in the 

 Earth's rotation. He concludes that the phenomenon is of 

 an order of magnitude which is not inconsistent with its being 

 due, in large measure, to such terrestrial movements of matter 

 as the melting of water off an elevated antarctic ice-cap or 

 to a sudden or gradual local rise or fall of part of the ocean 

 bottom. 



Stellar Motions. — During the past few months several im- 

 portant papers have been published dealing with this subject. 

 J. C. Kapteyn and W. S. Adams (National Acad, of Sciences 

 (Washington) Proceedings, vol. i. p. 14) have discussed the 

 relationship between the radial velocity of a star and its proper- 

 motion. They find that for all stellar types, the average 

 radial velocity increased very considerably with increase of 

 proper-motion. Since, on the average, large proper-motions 

 indicate nearness and low luminosity, whilst small proper- 

 motions indicate remoteness and great luminosity, this result 

 may mean that the average velocity of the stars decreases 

 with increasing distance from us, or that it decreases with 

 increasing luminosity, or that there is a correlation between 

 the different components of motion of a star. This result 



