Hi son1ofrover1, these are the first letters I have.
Hi cockie, as well as being a physicist I believe he is remembered more as an engineer and inventor.
A huge apology - I was reading down my list of actual letters taken from the clues, not the instruction itself!
Son...when I followed the instruction, it lead me to a longer than 10-letter word, but the puzzle is about physicists...
Like Cockie I am struggling to find the third one. Ginge's comment about him being an inventor as well made me think of the obvious American one but that didn't work. It is back to the drawing-board on this.