556 SCIENCE PROGRESS 



Stromgren, E., A New Class of Periodic Solutions in the General Problem 



of Three Bodies, viz. in the Problem of Three Bodies with all Masses 



and all Distances of the Same Order of Magnitude, M.N., R.A.S., 1919, 



80, 12. 

 Plummer, H. C, On the Ellipticities of the Maclaurin Ellipsoids, M.N., 



R.A.S., 1919, 80, 26. 

 Bell, H., A Proposal to Construct New Tables for finding Position Lines 



at Sea, M.N., R.A.S., 1919, 80, 72. 

 Conrady, A. E., The Five Aberrations of Lens-systems, M.N., R.A.S., 



1919. 80, 78. 

 Pettit, E., The Great Eruptive Prominences of May 29 and July 15, 1919, 



Astroph. Journ., 1919, 50, 206. 

 Evershed, J,, The Solar Prominence of May 29, 1919, M.N., R.A.S., 1919, 



80, 8. 

 Harper, W. E., The Orbit of the Spectroscopic Binary Boss 351 1, Pub. 



Dom. Obs. Canada, 1919, 4, No. 14 ; The Orbit of the Spectroscopic 



Binary 19 Lyncis, ibid., No. 15 ; The Orbit of the Spectroscopic Binary, 



h Draconis, ibid., No. 16. 

 Lunt, J., The Radial Velocities of 185 Stars observed at the Cape, Astroph. 



Journ., 1919, 50, 161 ; On the Spectrum of 77 Argus, M.N., R.A.S., 



1919. 79, 621. 

 Turner, H. H., and Blagg, Mary A., The Long- Period Variable W Cygni, 



M.N., R.A.S., 1919, 80, 41. 

 Plummer, H. C, An Analysis of the Magnitude Curves of the Variable 



Stars in Four Clusters, M.N., R.A.S., 1919, 79, 639. 

 Jordan, F. C, The Colour Changes of Certain Variable Stars of Short 



Period, Astroph. Journ., 1919, 50, 174. 

 Maggini, M., The Eclipsing Binary RR Vulpeculae, and the Evidence of 



Darkening towards the Limb, Astroph. Journ., 1919, 50, 141. 

 Heger, Mary L., The Occurrence of Stationary D-lines of Sodium in the 



Spectroscopic Binaries /3 Scorpii and 8 Orionis, Lick Obs. Bulletin, 



1919. 10, No. 326. 



PHYSICS. By James Rice, M.A.; University, Liverpool. 



Relativity. — In view of the widespread interest taken in this 

 subject by scientists and general public alike, it may not be 

 out of place to give a connected summary of this theory, thus 

 linking up and extending the references to it made by Mr. 

 Spencer Jones in the last number of Science Progress, and 

 by myself in earlier numbers. 



Relativity in its broadest aspect is based on the assumption 

 that all measurements and observations reveal only relations 

 between the object observed and the observer. In the special 

 physical sense, it is based on the complete absence of experi- 

 mental evidence that any dynamical, optical or electro- 

 magnetic effects arise from the motion of matter relative to 



