1. Of course a lead weight would fall faster than a feather , but that is only because a feather is slowed down by air resistance.

lead:heavy soft metal of dull greyish colour, used for water pipes, in roofing, as a radiation shield, etc and which is mixed with other metals to form alloys

2.If one carried out experiment with moving bodies on the train, all Newton's law will still hold.

hold: continue  to be true or valid

The offer I made to you last week still holds.

3. Because it did not accord with his ideas  of an absolute God

accord:(of a thing) agree or be in harmony with sth; correspond with sth

His behaviour does not accord with his principles.

4.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.

evenly:covering or affecting all parts of something equally

•Make sure the surface is evenly covered with paint.

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

eclipses:blocking of the light of the sun (when the moon is between it and the earth) or of the moon

6.. Nevertheless,Roemer’s achievement, in not only proving that light travels at a finite speed

finite:having an end or a limit

the earth's finite resources

7.Visible light has a wavelength of between only forty and eighty millionths of a centimeter.

the size of a radio wave used to broadcast a radio signal

8.Light waves should travel through the ether as sound waves travel through air, and their speed should therefore be relative to the ether.

the space through which radio waves or computer signals travel

voices coming through the ether

9.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.

postulate:put (sth) forward as a fact or accept (sth) as true, esp as a basis for reasoning or argument

The school building programme postulates an increase in educational investment.

10.Only light, or other waves that have no intrinsic mass, can move at the speed of light.

intrinsic: being part of the nature or character of someone or something

There is nothing in the intrinsic nature of the work that makes it more suitable for women.