382 SCIENCE PROGRESS 



atomic world which is being slowly built up, viz. the atomic 

 nature of angular momentum. Successes such as these do not 

 attend purely empiric assumptions. The whole of this work is 

 clearly pointing to the view that the structure of the atoms 

 of hydrogen and helium (the lightest atoms known) must 

 resemble closely the inner structure of all atoms, even the 

 heaviest, that region in fact which lies closest to the nucleus. 

 In the English Journals perhaps the most interesting paper 

 which has appeared in the past few months is one by Sir Oliver 

 Lodge. It will be found in the August number of the Phil. 

 Mag., and is followed by two communications from Prof. E. 

 Eddington on it, printed in the September and October numbers. 

 In this paper the author seeks to account for the well-known 

 discrepancy in the perihelion motion of the planet Mercury 

 by retaining the assumption of the fixed ether and avoiding 

 the relativity postulate. In the January number of Science 

 Progress there was a reference in these notes to Einstein's 

 gravitational theory founded on a generalisation of his original 

 relativity postulate, and mention was made there of the remark- 

 able success which this theory had achieved in removing this 

 discrepancy between the observed movement of the perihelion 

 of Mercury's orbit and that calculated on the usual Newtonian 

 principles as due to the perturbations of the other planets. 

 There is, unfortunately, no doubt that Einstein's method is not 

 easy to explain or grasp, while Lodge's suggested explanation 

 certainly is. It rests on the well-known assumption that some 

 part at least of the inertial mass of a body is of electromagnetic 

 origin, and that this electromagnetic inertia increases some- 

 what with the velocity of the body through the ether (assumed 

 stagnant). The solar system as a whole moves through space, 

 and so any planet must, during half of its rotation round the 

 sun, be moving relative to the sun in a direction making an 

 acute angle with the sun's way through space, and during 

 the remaining half its motion will make an obtuse angle ; hence 

 during one-half a revolution the planet's velocity through the 

 stagnant ether will be greater than that of the solar system as 

 a whole ; during the other half it will be less. Thus the inertial 

 mass of the planet will vary, increasing and decreasing alter- 

 nately above and below an average value. If now, as Lodge 

 assumes, this variable part of the inertial mass is unaffected 

 by gravitation, the gravitational attraction is constant at the 



