I'd like to make a circle that other people can subscribe to in Google+.  For my specific example, I know a few of my friends are interested in the fantasy series Wheel of Time and I'd like to add them to a circle so I can update just those people on my progress in the series.  Is there any way (other than broadcasting a message to everyone and just asking them, then adding them manually) to make the circle public so that other people who follow me can opt in to get updates to that circle as well?
Can I make a public circle in Google+?
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