MATTER, SPACE, AND TIME 253 



earth. It suggests that the aether is carried 

 along with the earth, a conclusion apparently 

 inconsistent with the astronomical evidence. 



The first successful attempt to explain this 

 discrepancy was made by Fitzgerald, Lorentz, and 

 Larmor. If the atoms of matter are electrical in 

 nature, or held together by electrical forces, it is 

 possible that matter may contract when it is 

 moving through the electro-magnetic medium or 

 aether. A very small contraction when matter 

 is moving through aether would suffice to explain 

 the facts, and the contraction could never be 

 observed directly, for all scales used to measure 

 it would undergo the same proportionate change. 

 It is probable that this explanation represents 

 one aspect of the truth. However this may be, 

 the velocity of light, as experimentally measured 

 by an observer, has always been found to be 

 3 X 10^^ centimetres, or 186,000 miles a second. 



Impressed by this experimental result, Einstein, 

 in 1905, accepted the constancy of the measured 

 velocity of light as an ultimate fact of Nature, 

 and was hence led to see that real experimental 

 space and time are always relative to some 

 observer, and that the ideas of absolute space and 

 time are mere figments of the imagination. 



By length or distance we always mean a 

 quantity arrived at by measurements made with 

 material or optical appliances by some particular 

 observer. Thus, we see that the length of a rod 

 is not an absolute property of the rod, but is a 

 relation between the rod and the observer. If 

 they are moving together, the length seems in- 

 variable, but, if the rod is moving past the 

 observer, it suffers the contraction suggested by 



