I was a student of Prof.Shewmon during1980-83, and a good friend of Paul from 1984!

I learnt a lot from Paul over the years...to list a few... I learned

1) that one can learn about anythiing, at any age, & from anyone!
2) to list things (numbered, like this!) even in an email message...
3) you can convey a lot with few words..

He called at odd times and came right to the question (as pointed out by J.Hirth)
Later this became emails.  I prepared short excerpts from my exchanges with him over the past 3 years, but dont know how to attach it here. If you saw it, you will see that he never stopped learning, asking questions, and often wrote with few words. 

His treatise on Diffusion had only 203 pages !

I quote below two of my personal favorites.

after a trip to India in 1980s -   "The cars took a reasoned view of the lights"

after hearing of my dad's passing last year  - "I watch, I wonder, and I wait"             
 
Tap - Christmas day 2015 

Paul was a runner in high school.  He made it to the State Meet in High School, and once told me (only in answer to my question), that he had run the mile in 4 minutes, 44 seconds.  I am sure it was a bit disorienting to him that I, as his first child, ended up with the dubious distinction of having gone through 3 seasons of Little League Baseball and never having hit a fair ball. It turned out only later that they found out I had double vision when I looked to the side, and that I couldn’t figure out which ball to hit.  Paul and Dorothy’s response was to try a different sport, and from the age of 8 years, we began to ski as a family.  I remember being sent off for the whole day with Joan, to go skiing in the Harz mountains.  We would leave from the town square in Göttingen, and with the rest of the kids, we would get packed onto a bus for the trip.  We spent all day walking up and skiing down the hills.  It was beautiful and fun.  And it began a family tradition that continues to this day. 

 Moving from Pittsburgh to Chicago threatened to be a setback for skiing, as Joan and I pointed out that it was about as flat as a table in Illinois.  But he responded by signing us up for a ski trip each year, usually in either Colorado or Utah.  He continued this generous habit long enough to also help start the next generation skiing, and both Ruth and Nate are expert skiers as a result.  

 He certainly also enjoyed hiking, which we did frequently as a family.  I think he also spent a fair amount of time around conferences in beautiful places taking his hiking equipment out to sleep under the stars.  He and I climbed up Mt Rainier on one of these adventures, a defining moment of my teen-age years.  

 Paul also enjoyed biking, and I think for much of his career at OSU (?) he biked to and from work.  If I have my story straight, his department gave him a bike as a present when he retired.  He used it to start signing up for 500 mile, 10 day bike trips, the most notable of which took him up and over the Pyrenees.  It was only after he fell from his bike (amazingly not breaking his hip in the process) in the Garage at the house on Postlewaite that he gave up biking.  We tried considering getting a tandem bike that would let him ride reclining in front, but he declined.  He was already starting to tire too much, and was into his last physical battle, with Parkinson’s disease.  His physical strength and endurance was part of what helped him live so long with this disease.  It came from a long love affair with physical activity. 

I think we all got calls that were remarkable one way or another.  Rather than the late night ones, I often got early morning calls.  For example, around 7AM, Saturday morning he would call, and as Marty Hirth mentioned above, he would start right in without introduction:  "how does your finger know how far to grow back after you cut the tip of it off with an axe?" (!!).  It was a fundamental question of biology, but it led to some questions about using an axe in the dark, as I later learned from my brother Andy, who witnessed the event.  Another time it was to tell me a story about his determination to become immune to poison ivy.  He gave himself a good stiff immunizing dose by working with it all day in the garden... after about an hour of walking around the neighborhood in his pajamas at 1AM, he ended up in the Emergency Room to get treated with a round of steroids.  As Kaan Erdal pointed out, he was a busy guy, and didn't sleep as much as the rest of us.  He was busy the rest of the time experimenting with the world.

Paul and I started as rookie professors at Carnegie Tech and later together at OSU.  Our family and his were friends. Llate at night, often very late once we moved West, I would get a call from him.  Without a salutation he would ask about some arcane point of science, eg "about the hydrogen distribution---".  Marty would know who had called without asking.  We are sad to hear of his passing but happy to have known and interacted with him.

Best to the family,

John & Marty Hirth

Grandpa Paul's cookie recipe:

OATMEAL COOKIES

2 cups brown sugar
2 eggs,
1 cup veg. oil (soybean, or canola)
1 tsp molasses
1 tsp vanilla
half cup walnuts, chopped
1.5 tsp. baking soda
half cup yellow raisins
Mix

2 cups flour
3 cups rolled oats
Mix well, form into 1 in. ball (we use a small dipper), dip/roll in dish of sugar, bake at 375 F 15 min. on oiled cookie sheet.

It was fun to visit Paul and Dorothy's house when I was a kid in the 90's. While the adults talked, my brother and I would sneak off and explore their basement full of trinkets collected from every corner of the world. Paul had rasberries growing in the backyard, and he would come out and pick them with us. He used to bake these molasses cookies, too.  They would come out of the oven nice and soft, but he liked them crunchy so he'd set them out for days until they were rock-hard.  Even so, the cookies were delicious.  I'll always remember them.