I went to Kings College and I first met Felix when I was a third year maths undergraduate in the early 1980's.
To help with choice of course for the final year, we were given a series of short talks by faculty members.
Felix came into the room and described his tensor calculus course in his typically clear and lucid manner - I am so glad that I decided to take his course. I count myself very lucky to have been taught by Felix.
His lecture style was informal, insightful and sometimes amusing, I recollect him explaining that he and a research colleague ( possibly Bondi ) had occasion to discuss tensor equations on the phone. And to facilitate the conversation they hit upon the idea of raising and lowering the pitch of their voices to correspond with "up" and "down" covariant/contravariant indeces!
He would also often drop in throw-away asides during classes - I recall him mentioning that Leopold Kronecker went mad in later life. I looked into this, and, yes, Kronecker did indeed hold some interesting opinions.

After I graduated, I received an unexpected letter, it was from Professor F.A.E. Pirani.
The content of the letter was to assure me that I had done well in his course and that the class of degree that I was awarded did not entirely do me justice. It was this act of kindness that led me to maintain a friendship with Felix over the years. I have some really nice memories of visiting Felix which I would like to share.

The first time I visited Felix, upon leaving, I said "Goodbye Prof Pirani", and he said, "Call me Felix - and that's an order!"

During one conversation, I asked him to explain his title at Kings which was "Professor of rational mechanics".
Felix explained that "Rational mechanics" was a term used by Newton to mean theoretical mechanics (as opposed to spanners etc which are practical!). And the reason he chose this title was that he felt that he was not really a pure mathemetician, rather, he was a "talented amateur"...

When I became a father, Felix was very keen to meet my wife and baby and we visited him - I have a picture taken circa 2004 that I will try to post. Felix showed great interest in our daughter and also my wifes job in the NHS.

Later, Felix and my wife conspired together on a birthday present for me - a Mosaic which hangs on our wall. We also visited his mosaic workshop to see his work.

My last communication from Felix was a Christmas card in which he suggested that we really should visit him in the comimg year so he could see how "the lovely Lucy" had grown up. I regret that 2015 was a busy year and I failed to make that visit.

Felix Pirani - we will miss you.

Steve Robinson, Ann and Lucy