Well, cbsailor got the location, though no extra credit.
aduffE37 - no, one is not broken. Duh.
Bill Roosa - I guess you could do a horizontal angle to figure distance off, but it would be rather complicated unless you knew that you were perpendicular to a line drawn between them. Otherwise, the angle would vary from zero if they were in-line (one behind the other) to some maximum value if you were perpendicular to them.
Actually according to one source, they were placed so that sailors could line them up like a range and then know what direction north lay. I suppose if your compass was broken in a storm that info could be useful.
See the link below for even more than you ever wanted to know about the Thacher Island lights.
http://www.lighthousefriends.com/light.asp?ID=475