Screen Couple Chemistry

Screen Couple Chemistry is one of the most difficult task as faces by a maker of a film: this is to thrill the senses and stimulating the imagination --but which, because of the emotional basis of our response, constantly evades scrutiny.
The phenomenon which described as the screen magic is hard to define but definitely know it when see it. I understand, this 'chemistry' is something that has been little discussed by film scholars. But it deserves in depth discussion and research.