clear round sphere's about the size of a soccer ball or larger floated slowly by

It was a hot summer's day , my sister and I were behind the shed sneaking a smoke when all of sudden two round balls that were about a foot wide floated slowly past us. The best way I can describe this was like the ball that floated on the Wizard of Oz that had the good witch Glenda in it. We lived out in the country at the time. there is no swamp near us. I had the feeling it was something that had control to it.
We watch it for about 5 min. untill we could no longer see them.
 We ran in the house and told our father and he said it was just probably swamp gas?
Witness indicates that the date of the sighting is approximate.  PD