THE ETHER AND MOVING MATTER 113 



appear as rather startling assumptions; but it is only in this man- 

 ner that present observational facts can be reconciled with a quies- 

 cent ether. With each advance in experimental refinement, theory 

 has had to adapt itself by the adoption of new hypotheses. This has 

 now been done up to second order phenomena for a quiescent ether. 

 Thus far, however, no hypothesis has been brought forward to adapt 

 specifically the theory of a quiescent ether to observations which have 

 already been carried up to the third order of the aberration constant. 

 The first second order experiment was carried out by Michelson 

 and Morley, and was an optical test in which the method of interfer- 

 ence of two rays passing over paths mutually at right angles to one 

 another was used. The apparent intent of the originators of this 

 experiment was initially to look for a first order change in the aberra- 

 tion factor by means of a second order interference effect. The diffi- 

 culty in reconciling the negative results of this test has, however, 

 given rise to hypotheses involving second order dimensional factors, 

 so that from this point of view it becomes a second order experiment. 

 It could not, however, show a first order change in the velocity of the 

 moving system, which latter, referred to the velocity of light, is taken 

 as a magnitude of the first order, and hence the former change would 

 count as a second order magnitude. In this experiment the entire 

 system was mounted on a float so that the optical system could be 

 rotated consecutively through all quadrants of the circle while the 

 interference bands were being continuously observed. If now the 

 difference in time of passage of one of the rays, say along the line of 

 drift, and the other at right angles to it, is calculated on the basis 

 of a moving ether, we find it to be equivalent to the time of passage 

 over a length corresponding to a diminution of this length, in the 

 direction of drift, proportional to the square of the aberration. Their 

 results show that had there been an effect, it must have been probably 

 sixteen times, certainly eight times, less than that calculated. It is 

 understood that Morley and Miller will soon report as the result of 

 a repetition, during the present year, of this experiment on a much 

 larger scale, that, if there is any effect, it must be one hundred times 

 less than the calculated value. This result is entirely consistent with 

 a moving ether, but seemingly contradictory to a quiescent ether, 

 as proposed by Fresnel. Apparently, then, either some condition in 

 the fundamental hypothesis of such a medium has been overlooked, 

 or a supplementary hypothesis must be imagined. Similar hypotheses 

 were conceived of by both Lorentz and Fitzgerald independently, 

 shortly after the publication of the experiments of Michelson and 

 Morley in 1887. They assume that a contraction in the direction of 

 motion takes place in a system moving through the ether, so that this 

 dimension is reduced by a fraction of itself equal to one half the 

 square of the constant of aberration. This of course, as an assump- 



