Numix Icon Theme Circle is a popular, beautiful icon theme for Gnome desktop. But, it also compatible with Unity and other desktop environment. Here we provide the download link or we will show you how to get the most recent version of Numix Icon Theme Circle from Github.
First, make sure you have git package installed. On Ubuntu, you can use this command to install git
sudo apt-get install git
Now download the Numix Icon Theme Circle package using this command
git clone https://github.com/numixproject/numix-icon-theme-circle.git
Once downloaded, you have to move the Numix folder to /usr/share/icons. And then use Gnome Tweak Tool or Unity Tweak Tool to change the system icon theme.
Alternatively, you can use the following PPA on Ubuntu
sudo add-apt-repository ppa:numix/ppa
sudo apt-get update
sudo apt-get install numix-icon-theme-circle
Have a try.