http://books.google.com/books?id=JokgnS1JtmMC
"Relativity and Its Roots" By Banesh Hoffmann
p.92: "There are various remarks to be made about this second
principle. For instance, if it is so obvious, how could it turn out to
be part of a revolution - especially when the first principle is also
a natural one? Moreover, if light consists of particles, as Einstein
had suggested in his paper submitted just thirteen weeks before this
one, the second principle seems absurd: A stone thrown from a speeding
train can do far more damage than one thrown from a train at rest; the
speed of the particle is not independent of the motion of the object
emitting it. And if we take light to consist of particles and assume
that these particles obey Newton's laws, they will conform to
Newtonian relativity and thus automatically account for the null
result of the Michelson-Morley experiment without recourse to
contracting lengths, local time, or Lorentz transformations. Yet, as
we have seen, Einstein resisted the temptation to account for the null
result in terms of particles of light and simple, familiar Newtonian
ideas, and introduced as his second postulate something that was more
or less obvious when thought of in terms of waves in an ether. If it
was so obvious, though, why did he need to state it as a principle? ...
