But then, got off on a vacation trip, and was studying bird flight, just for the fun of it, and you can watch a bird soaring around in circles, and measure the time, and estimate the bank angle, and immediately, figure out its speed, and the turning radius, and so on, which I could do in the car, as we're driving along on a vacation trip --  -- with my three sons, young sons, helping me,
后来我做了个度假旅行，学了一些鸟类飞行的知识， 纯粹是感兴趣而已。 你能观察一只鸟打圈飞翔。 测量时间，估计倾斜角， 马上就能知道它的速度， 转弯半径什么的。 我在去度假旅行的路上，开车的时候就玩这个。  同行的有我的三个儿子，都还年轻，帮着我，