Fill in the blank (scientists): 21 questions

Fill in the blanks with the surnames of scientists, astronomers, mathematicians etc.

I was in a shop looking at a bicycle I was thinking of buying. I had taken up cycling after giving up gymnastics. I was very good on the rings, but useless on the pommel horse and a very poor (1).

I asked if it had a (2) but the assistant replied “Sorry, it’s got (3). Are you buying it for yourself?”.
“Yes, it’s (4)”.