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Published online by Cambridge University Press: 14 August 2015
Time and again Dr. B. Bok publishes his reviews on the state of optical searches of the spiral arms in our Galaxy. A great optimist at the beginning, concerning the agreement of different results, he became later more critical in his conclusions. But in his paper of 1967 he claims anew, as well established, that we can trace the spiral arms up to a distance of 14000 pc from the centre.