Einstein - speed of light

[volvo179]

why is "c" in Einstein's equation the speed of light?

[CT]

Is that, why is it the letter 'c' or why is it the speed of light?

[scubadiver]

If it's "why is it the letter c ?"-then that is because "c" stands for  a "constant", ie, the speed of light.

If it's "why is it the speed of light ?" - it needs to be, to make that particular theorem work!!

[THECORBYLOON]

"As for c, that is the speed of light in vacuum, and if you ask why c, the answer is that it is the initial letter of celeritas, the Latin word meaning speed."

Isaac Asimov in "C for Celeritas (1959)"

[volvo179]

Sorry my question was ambiguous and thanks for the responses.  Scubadiver can you elaborate on your response that the speed of light was chosen to make the e equals mc squared equation work.  Given that a small amount of matter contains a massive amount of energy the constant in the equation is always going to be very large but why the speed of light rather than any other large constant?  I assume that post Einstein experimental data has been obtained that validates the theory but when Einstein proposed the theory what was it that led him to think that the speed of light was the appropriate constant?