CAUL for sale!!!

This is from the first Chapter of David Copperfield..

"I was born with a caul, which was advertised for sale, in the newspapers, at the low price of fifteen guineas. Whether sea-going people were short of money about that time, or were short of faith and preferred cork jackets, I don't know; all I know is, that there was but one solitary bidding, and that was from an attorney connected with the bill-broking business, who offered two pounds in cash, and the balance in sherry, but declined to be guaranteed from drowning on any higher bargain."

My question is simply this. Why would anyone buy a caul???
I didn't really even know what it was until I looked it up in the dictionary. It seems to be some growth over the head of a baby growing in the womb.

Does anyone know why anyone would wish to purchase something like this? Was there any use for it or some superstition that went along with it? It seems as though (from the text) it was used by people that spent time in the sea. Just curious about this. It's kind of weird.

It was thought to protect a persom from drowning the way it had proteted the child in the womb.... Its actually part of the amniotic
sack if I rember correctly without looking it up.
If you look at the pargraph again it actually explains it in round about way.

I've always heard that anyone born with a caul would have second sight. Also, it was considered very good luck. I haven't seen or head that word in years!