Subject: What am I doing incorrectly? (Potato Electricity Lab)

I am conducting this experiment: http://www.madsci.org/experiments/archive/889917606.Ch.html
and it does not seem to work with my materials. I have done as listed
1. Inserted a galvanized nail with copper wire wrapped around it into one end of the potato
2. Inserted a similar size piece of copper wire with copper wire wrapped around it into the other end 
of the potato.
3. I have connected the 2 pieces of wire at the tip of an assorted amount of lightbulbs, to no avail. 

Am I doing something wrong? I would like to know ASAP about what I need to fix, as my project is 
due in a little more then 1 month!

From, 
Ben

Re: What am I doing incorrectly? (Potato Electricity Lab)