Performing the installation process described here: https://ethereum.gitbooks.io/frontier-guide/content/installing_linux.html
Why am I getting these error messages?
W: Failed to fetch http://ppa.launchpad.net/ethereum/ethereum-dev/ubuntu/dists/jessie/main/binary-amd64/Packages 404 Not Found
W: Failed to fetch http://ppa.launchpad.net/ethereum/ethereum/ubuntu/dists/jessie/main/binary-amd64/Packages 404 Not Found
I'm relatively new to Linux so it's very possible that I've missed something fairly basic. Any help would be much appreciated. Thank you.