words and expressions

1.unambiguously adv.

they believed that one could unambiguously measure the interval of time between two events

2. finite n.

The fact that light travels at a finite, but very high, speed was first discovered in 1676 by the Danish astronomer Ole Christensen Roemer.

3.moon n.

He observed that the times at which the moons of Jupiter appeared to pass behind Jupiter were not evenly spaced, as one would expect if the moons went round Jupiter at a constant rate.

4.evenly adj.

5.eclipse n.

Roemer noticed that eclipses of Jupiter’s moons appeared later the farther we were from Jupiter.

6. propagation n.

A proper theory of the propagation of light didn’t come until 1865.

7.ripple n.

a small wave or undulation, as on water

like ripples on a pond

8.crest n.

the distance between one wave crest and the next

9.infrared 

Shorter wavelengths are known as microwaves (a few centimeters) or infrared (more than a ten-thousandth of a centimeter).

10.motion n.

They compared the speed of light in the direction of the earth's motion with that at right angles to the earth's motion

11.contract

Between 1887 and 1905 there were several attempts, most notably by the Dutch physicist Hendrik Lorentz, to explain the result of the Michelson-Morley experiment in terms of objects contracting and clocks slowing down when they moved through the ether.

12.clock v.

13. hitherto adj.

However, in a famous paper in 1905, a hitherto unknown clerk in the Swiss patent office, Albert Einstein, pointed out that the whole idea of an ether was unnecessary.

14.postulate n.

The fundamental postulate of the theory of relativity, as it was called, was that the laws of science should be the same for all freely moving observers, no matter what their speed.