March 26, 1920] 



SCIENCE 



311 



to the fact. It would be of great importance 

 to know, of course, whether as the distance of 

 a star from the sun greatly increases, the de- 

 flections of light will correspond more and 

 more closely with that given by cause a. There 

 is no possibility that the Einstein effect with 

 increased distance will merge into the New- 

 ton-Maxwell effect, since theoretically the 

 former should always be twice the latter. 

 However, if the main cause of light deflections 

 should prove to be a, c and e, or a and e, or 

 similar ones in effect, it may be possible, as 

 already stated, to harmonize Dr. Campbell's 

 results with those of the British observers. As 

 a caution it may be well to bear in mind that 

 Dr. Campbell unfortunately was obliged to 

 get his results from very distant stars and 

 hence had to look for quantities very much 

 smaller than those concerned in the British 

 observations of the solar eclipse of May 29, 

 1919. 



OUTSTANDING MOTION OF MERCURY's 



25. As a further proof of the Einstein 

 theory of gravitation has been cited the very 

 satisfactory way°° in which the theory ac- 

 counts for the outstanding motion of the peri- 

 helion of mercury, characterized by the late 

 Professor Simon Newcomb as one of the 

 greatest of astronomical puzzles. Dr. Charles 

 L. Poor, of Colimibia University, at the close 

 of my lecture there on January 16 suggested 

 that the outstanding motion of Mercury's 

 perihelion could also be fully accounted for 

 if the equatorial radius of the sun were found 

 to exceed the polar radius by 0".5, so that the 

 sun would not be truly spherical. Seeliger 

 advanced the hypothesis^^ "that the scattered 

 zodiacal-light materials, if condensed into one 

 body might have a mass fairly comparable to 

 that of the little planet Mercury, " and he has 

 concluded that the attractions of the zodiacal 

 light materials upon the planet Mercury could 

 explain the deviation of that planet from its 



20 See A. S. Edddugton's Report on The Eela- 

 tivity Theory of Gravitation, London, .1920, p. 52. 



21 W. W. OamplDell, "The Solar System," pnb- 

 Uslied in The Adolfo Stahl Lectures, p. 10, San 

 Franciaoo, 1919. 



computed orbit. This problem can not yet be 

 regarded as definitely settled." 



EINSTEIN DISPLACEMENT OF LINES OF SPECTRUM 



26. Dr. Einstein appears to regard as es- 

 sential to this theory the verification of the 

 shifting towards the red of the lines of the 

 spectrum of light from the sun and stars. 

 However, Sir Joseph Larmor, according to a 

 paper presented before the Eoyal Society on 

 November 20, 1919, does not apparently agree 

 with him. The predicted effect has not yet 

 been successfully observed, or, as Professor 

 Joseph S. Ames in his concluding remarks 

 at the end of my lecture at the Johns Hopkins 

 University put it, " has not yet been disen- 

 tangled from the various possible other causes 

 for shifts of the spectrum lines." 



CONCLUDING REMARKS 



27. The endeavor has been to set forth im- 

 partially all the facts pro and con with refer- 

 ence to the question of the verification of the 

 Einstein theory of gravitation by the recent 

 astronomical observations, so as to enable the 

 reader to form an independent judgment and 

 reach his own decision. Though we may 

 differ as to whether the Einstein theory has 

 been definitely verified, or not, one result of 

 fundamental importance appears to have been 

 established with fair certainty, upon which 

 perhaps chief emphasis should be laid, viz. : 

 that light has weight — just how much depends 

 upon whether the Newtonian or the Einstein 

 principles will ultimately be found correct. 

 Possibly the best attitude to take is that of 

 open-mindedness and to let no opportunity 

 pass by for further experimental tests. The 

 British astronomers are already zealously pre- 

 paring to make observations during the solar 

 eclipse of September, 1922, which will occur 

 in Australia. Perhaps one of the most satis- 

 factory residts of the discussion aroused by 

 the subject has been the stimulus imparted 

 to further research in many fields, which is 

 bound to bear fruit. Louis A. Bauee 



Department of Terrestrial Magnetism, 

 Carnegie Institution op Washington 



