y. 



494 H. A. Bumstead — Lor entz-Fitz Gerald Hypothesis. 



material objects, but when all the apparatus concerned as well 

 as the observer are carried through the ether with the velocity 



The effects to be expected are of the order -of l^J ; this 



is a very small fraction even when v is the velocity of the earth 

 in its orbit, but the possible accuracy of certain optical experi- 

 ments is so great that these effects could certainly be found if 

 they existed without some compensating effect to mask them. 

 As is well known, these effects have never been found ; the 

 first conclusively negative results were obtained in the cele- 

 brated experiments of Michelson and Morley,* and several 

 other optical investigations have also failed to show the expected 

 results. On the electrical side the problem has been attacked 

 by Trouton and Noble, f who hung up an electrical condenser 

 by a torsion wire and looked for a torque which, on the. theory 

 of a stagnant ether, ought to exist when the condenser is car- 

 ried along by the earth. Although the sensitiveness of their 

 experimental arrangement was ample for the observation of 

 the expected second order effect, their result was also negative. 

 The most obvious interpretation of- these results is that the 

 ether near the earth has the same velocity as the earth ; but, 

 as has been stated, it appears to be impossible to reconcile this 

 view with the great mass of optical and electro-dynamic evi- 

 dence. The only satisfactory way out of this difficulty which 

 has hitherto been suggested is a hypothesis put forward in 

 1892 by Lorentz,;); and which had been independently sug- 

 gested but not published by FitzG-erald. According to this 

 hypothesis, when any material body moves relatively to the 

 ether its linear dimensions parallel to the direction of motion 



are contracted in the ratio of \y i__ ^L to 1, while the dimen- 

 sions perpendicular to the direction of motion remain unchanged. 

 If this contraction takes place in the interferometer of 

 Michelson and Morley and in the condenser of Trouton 

 and Noble, their negative results are entirely explained on the 

 theory of a stationary ether.§ As Lorentz points out, this 

 contraction will be very small in any motions of material 

 bodies which we can observe ; for example the diameter of the 

 earth in the direction of. its orbital path will be diminished by 

 only 6'5 cm by its motion. It would moreover be impossible to 

 detect the shrinkage, however great it might be, by ordinary 



* This Journal, xxxiv, p. 333, 1887. 



f Phil. Trans. R. S. (A), ccii, p. 165, 1903. 



i Versl. Akad. Wet. Amsterdam, 1892-3. 



§ See Lorentz, Versuch einer Theorie, etc., §89. Amsterdam Proceed- 

 ings, 1903-4, p. 809, reprinted in Ions, Electrons, Corpuscules, vol. i, p. 477. 

 See also Larmor in FitzGerald's Collected Papers, p. 566. 



