Vintage Glass Insulators once were used on every electric, telephone and telegraph pole to keep everything safe and dry. They can still be seen now and then on poles where replacement has not been called for. Insulators are a big field for collectors and recently designers who are re-purposing them as all sorts of lighting, bookends, garden decor and more!
I purchase 3 clear ones recently to be added to vintage yard art projects.
There is a huge amount of information about these everyday treasures and the folks who collect them here: http://www.insulators.info/
More of the letter I at ABC Wednesday : http://abcwednesday-mrsnesbitt.blogspot.com/