The boys are 5-1/2 years apart in age, and they haven't always been close. There were a couple of years, in fact, where arguments were a daily occurance.
But as with so many things related to children, it pays to wait. Now 12 and 18, they interact constantly; and I love seeing how their interactions feed each other.
For example, S found the above book one afternoon and began browsing. At first, he was disappointed. "Why is it called Backyard Ballistics if nothing in here explodes?"
C explained the difference between ballistics and explosives. Overnight, it seems, C has become both mentor and teacher to S. He shares with his brother vocabulary, music and computer knowledge, and his interests in politics and history. S has so far not had C's inclination toward devouring news and non-fiction reading, so this is a natural way for him to be exposed to what he might not otherwise take in.
What S leans toward naturally is making things. When he decided he wanted to make one of the projects in the book, I asked him to give me an estimate of what it would cost. This isn't contrived mathematics on my part—he wanted to have it funded. So with his brother's help, he made a materials list, along with estimated costs; I gave the boys a little money, and together they went shopping.
I'm not entirely certain that this project wasn't chosen due to its requirement of empty Pringles cans.
Once the potato chips were eaten, C lost interest; S assembled the unit with help from DH.
You can barely see it, but the photo below shows the tennis ball popping out of the mortar. First try, and it worked! S was thrilled.
He shot the ball out over and over all afternoon, and C came back out and admired his work. These immeasurable moments are why a lot of us homeschool. Trajectory angles come and go, but family is something we hope will always be there.
Right now we still have very much an older and a younger brother, but their age gap will narrow soon enough. If they are lucky, this relationship they are building will give them a place from which to teach, learn from, and encourage each other over the years. That would be enough for me.