Before there were salt shakers, there were "salt dips", and if you can't visualize what a glass salt dip looks like, I'm here to help in that department:
I should note that not all salt dips, sometimes called "salt cellars" or "open salts", are glass. Many times they are silver, porcelain, and less often, wood. I just happened to have a plethora of glass salt dips I purchased recently from my friend Sharon. They make a fun collection because of all the various shapes and patterns. Some are footed, some are not:
Salt used to be a big deal because it was precious. A large salt, called a "trencher salt" or "master salt" was placed in the center of the table, and the individual salts could be re-filled from it. A small silver spoon was used for this function, and the little spoons themselves are quite collectible.
Below is the master salt on the left, next to an individual salt dip so you can see the difference in size:
You might be wondering, "Why did it take so long to invent the salt shaker?" And that would be a good question! Up until World War II or thereabouts, salt was sold in blocks. There hadn't been a way discovered to sell it without deterring moisture affecting it at the store or once the consumer got it home. Once put in a shaker, it would have turned into a lump. With the additive magnesium carbonate, salt could be sold in granules that would pour even in humid conditions. Remember the Morton Salt slogan "When it Rains it Pours"? That's when people began ditching salt cellars and using salt shakers.