Artificial Harmonics

i've always listend to randy rhodes and eddie van halen and they clan play like artificial harmonics really fast it's crazy. First of all can someone explain how the artificial harmonic is pulled off. they say to take your middle fineger and thumb and play the note, and gently place your index finger on the string to create a high pitch. Well i tried it and sometimes i acheive the effect sometimes not. I wonder how they do it so fast.

It's explained right here:

http://www.electricblueseuphoria.com/DAB/artificialharmonics4dummies.jpg

There's a diagram I drew to help visualize the concept.


Matt