If you want mail to be delivered from 2 to 1 as it arrives (or vice versa, from 1 to 2, but obviously not both directions), then you’re in the wrong place. You want to be in the tab for “Forwarding and POP/IMAP” to enable mail to be sent to one address and instantly appear in the other.

Go into account #2, click on the little wheel in the upper right hand corner, select Settings then choose the tab for Forwarding and POP/IMAP. Right at the top of the page is an area to forward the mail to another email address. I do it to forward my mail to work all the time.

I had the same problem with my gmail. It was easy to take from yahoo, to google, but not google to google.

You can also do it easily by creating a filter in your second email address.
1) Click on “create filter” at the top of the screen
2) In the filter dialog box, enter your second account address in the “TO” field. Click “next step”
3) Put a check by “Forward it to” and enter the email address for Account #1 (You can also choose to apply a label like “forwarded” at this step
4) click “Create Filter