Jumping in an oven

It was hot today.  Hot and still, so the air was heavy and thick.  Duke doesn't care much for heavy, hot, still, thick air.  He suggested, as we warmed up, that we should take one of the exits out of the jump arena, each time we went past.  I told him it would be worth it to wait and jump in the lesson and it was.
John had us start with just a bit of trot and canter, and he said to work more on getting the inside leg to outside hand connection, and then work on the inside bend.  When I used the diagonal aids, Duke got much more round than when I just used one.
We jumped a cross rail, then went right away to a vertical that had two ground poles and two guiding rails, making a chute.  Duke kind of clobbered his way through it the first few times, but when I didn't help him out, he decided to figure it out himself, and then we rode through it like it was a breeze.  Afterwards, John said that was a good decision to make, but it really felt like the only decision I could make - I'm not good enough to help him with each foot step, and I'm willing to go down with him if he doesn't figure it out on his own.  I'm glad he does though, because it felt great once he got it.
My job was just to count and try to keep the rhythm - 1-2-3-4-1-2-3-4 - although I did do a little bit of counterbend before the first turn and some teeny tiny half halts on the way in to balance him and keep him uphill and light, instead of letting him dive down and long and flat.
From there, we did a little oxer off the left lead, which rode pretty well.  But when we got a funny distance, John said keep the rhythm but make the canter bigger, and then you can add or you can go long.  So first we went long and then we added.  As much as I prefer to go long, adding felt a bit more comfortable.
From there we did a course - left lead over red oxer, right hand turn to black vertical, decide 7 or 8 to oxer (John made this because of the issues with the 5/6 line at Rebecca), left hand turn around the cross rail to plank vertical, three tight strides to an oxer (the best line we rode), right hand turn back to the ground poles and the chute (Duke scrambled through it again), right hand turn to a roll top with a vertical on it.
John said not to chase him.  That I can use leg and make his strides longer, but don't chase him into a long flat jump, because he likes to dive down and its unpleasant to ride compared to when he's uphill. It's ok to adjust strides when I see the distance is wrong, but keep the rhythm.  It was so easy to tell that John had been riding him because it felt the nicest I've ever ridden him over fences.
He said when Duke was there last week, and what I've experienced this week - he just really doesn't like the heat and gets uncomfortable.  John thinks it's his thin skin, like when you're a kid with the sweat and salt dried on you but you're wearing a shirt so you think the shirt is itchy. Duke kept stomping his left front foot, which I've never seen him do before.
Man, that was some nice jumping.  It made my whole week.