What does "bon nuit mon cherie" translate to?

Bon nuit, mon cherie would translate as - Good night, my darling. 
It is a French expression you use when you want to tell someone to sleep tight, basically. 

Gasses as an state of matter are far apart and spread out.

1one sharp difficulty presented itself. in the intervening twenty-five years my name had become reasonably well known.2 this being so, my trip demanded that i leave my name and my identity at home.3 i had to go alone and i had to be self-contained, a kind of casual turtle carrying his house on his back.4 with all this in mind i wrote to the head office of a great corporation which manufactures trucks.