In general, they are explained here:
http://en.wikipedia.org/wiki/Mnemonic
Here is a particular type where you count up the number of letters in each word to
get a digit. And this example also has to do with the meaning of what is desired
to remember (some digits of a number).
I have a root of a two whose square is two.
1 4 1 4 2 1 3 5 6 2 3
2 = 1.414213562373...
http://en.wikipedia.org/wiki/Mnemonic
Here is a particular type where you count up the number of letters in each word to
get a digit. And this example also has to do with the meaning of what is desired
to remember (some digits of a number).
I have a root of a two whose square is two.
1 4 1 4 2 1 3 5 6 2 3
2 = 1.414213562373...