96 SCIENCE AND METHOD. 



makes us believe that we think of an absolute space. 

 I was thinking of the earth's motion on its elliptical 

 orbit round the sun, and I allowed i8 miles a second 

 for its velocity. But its true velocity (I mean this 

 time, not its absolute velocity, which has no sense, 

 but its velocity in relation to the ether), this I do not 

 know and have no means of knowing. It is, perhaps, 

 10 or lOO times as high, and then the deformation 

 will be lOO or io,OCK) times as great. 



It is evident that we cannot demonstrate this de- 

 formation. Take a cube with sides a yard long. It 

 is deformed on account of the earth's velocity ; one 

 of its sides, that parallel with the motion, becomes 

 smaller, the others do not vary. If I wish to assure 

 myself of this with the help of a yard-measure, I shall 

 measure first one of the sides perpendicular to the 

 motion, and satisfy myself that my measure fits this 

 side exactly ; and indeed neither one nor other of 

 these lengths is altered, since they are both perpendic- 

 ular to the motion. I then wish to measure the other 

 side, that parallel with the motion ; for this purpose 

 I change the position of my measure, and turn it so 

 as to apply it to this side. But the yard-measure, 

 having changed its direction and having become paral- 

 lel with the motion, has in its turn undergone the 

 deformation, so that, though the side is no longer a 

 yard long, it will still fit it exactly, and I shall be 

 aware of nothing. 



What, then, I shall be asked, is the use of the 

 hypothesis of Lorentz and Fitzgerald if no experiment 

 can enable us to verify it ? The fact is that my state- 

 ment has been incomplete. I have only spoken of 

 measurements that can be made with a yard-measure, 



