just don't know how to deal with it

my son is alittle over 2  years and my daughter is almost 5 months . the problem is that my son is jealous and thats normal I understand that it happens to most kids and it has a logical reason..... sometimes when mom has to spend so much time attending the new arrival,  

what I need help on is how to deal with it because he sometimes hits her. Some times I catch him squeezing her hand, pulling her, pinching, and scratching. I know he dose'nt do it hard because he dosent want me to notice that he did anything to her but I dont know how to get him to stop