Oh look, the building is melting.... or am I experiencing a flashback?
Ni * Sin(Ai) = Nr * Sin(Ar)
where:
Ni is the refractive index of the medium the light is leaving,
Ai is the incident angle between the light ray and the normal to the meduim to medium interface,
Nr is the refractive index of the medium the light is entering,
Ar is the refractive angle between the light ray and the normal to the meduim to medium interface.