Ds1 is 3, and has not taken well to the arrival of his brother 3 months ago.
The hitting has lessened, but still happens a few times a day, often when I'm feeding him, or when he's asleep. He also tries to poke him in the eye a lot.
I am trying to stay calm about it, and mostly try and follow advice I read to ignore the hitter and give your attention to the one whose been hit, on the basis that ds1 is most likely doing it for attention. However sometimes he really makes him cry and I just lose it and yell at him which doesn't help anyone
the more he does it the more I find it hard to keep my cool. Eg today ds2 was dozing off in his bouncy chair, ds1 yelled that he wanted him awake and then just ran over and hit him hard around the head causing ds2 to really wail.
Ds1 has really struggled with the presence of his sibling and his previous good behaviour has gone down the toilet in lots of areas, but this is one I'm finding particularly hard to deal with as its my baby hurting my other baby 
Any advice?