RECENT ADVANCES IN SCIENCE 17 



that theory was given by Prof. A. S. Eddington at the week 

 evening meeting of the Royal Institution on February 1st, 

 1 9 1 8. This lecture was reprinted in Nature. 



The Origin of the Moon. — Sir George Darwin showed, on 

 his theory of tidal friction, that the earth and the moon were 

 once close together, revolving so that each kept the same face 

 towards the other. He supposed that the two had originally 

 formed one body, although the cause of the separation was not 

 traced, and that one of the free periods of vibration of a liquid 

 mass of the dimensions of the earth would not differ greatly 

 from half the initial period of rotation required by tidal theory; 

 the semi-diurnal solar tide would then be magnified by reson- 

 ance and might produce a rapidly increasing deformation which 

 might easily lead to a rupture of the mass into two parts. 



Bryan showed that this resonance theory of the origin 

 of the moon was not tenable if the earth was assumed homo- 

 geneous. H. Jeffreys has investigated the matter more 

 generally in a paper entitled " The Resonance Theory of the 

 Origin of the Moon," M.N., R.A.S., 78, 116, 1917. He shows 

 that homogeneity gives the most favourable case for instability 

 and the least favourable case for resonance, and that the period 

 of rotation necessary to give resonance for the semi-diurnal 

 tide raised by a fixed body can be made as long as one wishes 

 by suitable choice of the density distribution. He then examines 

 what takes place when resonance has been established. The 

 general problem is too difficult to attack, but special cases 

 are considered. It is shown that a deformation in the earth 

 comparable with its size would be formed, and that if the 

 deformation became great enough, a satellite would be formed. 

 As to whether the deformation could be great enough cannot 

 at present be answered. The theory therefore remains open 

 and Bryan's result cannot be regarded as disproving it. 



The following is a selection from amongst the more impor- 

 tant papers recently published : 



Theory of Errors. — Liapin, N., On a Fundamental Pro- 

 perty of Accidental Errors, Observatory, 41, 172, 191 8. 



Plummer, H. C, On the Errors in a Series of Tabular 

 Quantities, M.N., R.A.S., 78, 147, 191 7. 



Gravitational Astronomy. — Smart, W. M., Libration of the 

 Trojan Planets, Part I., Mem., R.A.S., 62, pt. iii. 191 8. 



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