The shell bone script of character Gas is
The Dictionary of Pictography (象形字典）explains that the top line is the sky, the bottom line is the earth, the middle line is the air. I think that the three lines are air flow or light cloud. But it is same as character Three, which is confusing.
The bronze script of the character is
air flow or cloud in the sky, big difference from the character three.
The big seal script of the character is