What is a vacuum tube?

Unless you are 60 or over you would not know what a vacuum tube is or what they are used for. The person has a storage shed with shelves of them. The bees thought that was a great place to live. All of that comb was built in a little over two weeks. I really dislike the waffle patterns that they use on the storage sheds, it makes it very hard to get the comb out. The bees fill the squares with comb.