how sceintists of 17-18th centuary measured the speed of light????they cannot do it by distance/time as then by the time they have measured 1s light would travel far ahead of them to mesure(300000km)..and they didn't have eqipments to measure 1/100000th of second that time..even if they did ,by the time they mesured it,it should move ahead.....so how did they managed to do it.. ???????? :confused: :confused:

pls help me out .....

Ole Roemer watched Io pass in and out of Jupiter's shadow, and noted that the time depended on how close Jupiter was to the earth, implying a finite speed.

 

Bradley used stellar aberration.

 

Wikipedia entry

swansont ,can you pls xplain it a little bit...how he used stellar aberration???

It's explained in the link, "aberration of light," within the article to which I linked. The angle of stellar aberration depends on the relation between the earth's speed and the speed of light.

Thanks for that Hyperlink + Information Swansont.