Oh boy; here we go!
Just about everyone knows that ladies in the 1800's wears a corset. Is that a safe guess? Believe it or not, the corset had more uses that cinching the waist.
The first most important one was that it was a bra. The funny thing is this did not occur to me until I started looking into one. And then I thought "Oh! Why didn't I realize this before?"
The second reason was to cinch the waist. There is a lot of controversy as to whether or not corsets affected ladies health. From my research, it could have. It depended on how young they really started cinching it tight, or exactly how tight they kept it. And yes, you can breathe in a corset. They made your waist smaller, but didn't squeeze your chest. Part of fashion was to have a big bosom and a small waist.
The third and last reason was back support. After a reenactment, my waist hurt from having so many layers (skirts are really heavy!). I have been told that the corset actually helps relieve all the weight. It also helps with posture.
One thing I did not know about corsets is that they actually can be done up in the front. Notice in the second picture those funny button-looking things. That part is called the busk; it was basically a hook and eye closure so ladies didn't always need help. It couldn't be laced as tight, and it would need to be re-cinched by someone else every couple days, but I thought that was pretty nifty.