[Proc. Rot. Soc. Victoria, 31 (N.S.), Part II., 1911)]. 



Akt. XIV. — Note on the Real Significance oj the Michelson- 

 Moiiey Experiment, 



By E. R J. LOVE, M.A., D.Sc. 



(University of Melbourne). 

 [Read 7th November, 1918]. 



In the year 1887, Michelson and Morleyi published their well- 

 known research having for its object the detection and measure- 

 ment of the speed and direction of the earth's motion relative to 

 the ether of space. The apparatus employed by them at the time 

 was fully adequate to their purpose; as subsequently modified by 

 Michelson,2 it became capable of affording measurements of con- 

 siderable precision; yet the result was uniformly null. 



Ihe obvious conclusion to draw was that the relative speed was 

 zero; i.e., that the ether in the neighbourhood^ of the earth is 

 carried along with it in its orbital motion. The difficulty of such 

 a conclusion lay in the fact that all other investigations, carried 

 out up to that — or even the present — date, go to prove that the 

 relative speed in question and the earth's orbital velocity are 

 indistinguishable; in other words, that the earth's motion leaves 

 the ether undisturbed. ^ 



In 1892, Fitzgerald^ and Lorentz^ independently suggested their 

 (now famous) "contraction hypothesis" as a way out of the diffi- 

 culty. This asserts that a material body, when set in motion, 

 undergoes a change of linear dimension in the direction of that 

 motion. As the phenomena of electrolysis had already proved the 

 mutual actions of atoms in the molecule to be, in part at least, 

 electrical, the occurrence of .some such change could hardly be 

 disputed; it only needed recognition; but its sign and amount 

 were alike undetermined by such phenomena as those of electro- 

 lysis. Fitzgerald and Lorentz accordingly suggested tliat the 

 change might, for adl that was known at the time, very well be a 

 contraction, of the right amount to account for Michelson and 



1 Phil. Mag. f\ .], xxiv., 1887, p. 449. 



2 Am. Journ. Sci. [iv.l, iii., 1897, p. 475. Maiiy later writers seem to have overlooked this 

 interesting paper. 



3 The term "neighbourhood," as the paper quoted in note 2 shows, must be liberally inter- 

 preted. 



1 Which is not quite the eame thinjf as saying that the ether is at rest In space. 



5 Nature, xlvi,, 1892, p. 165. 



6 Versl. d. k. akad. van Wet., 1892-3, p. 74. 



