Owing to the fact that a Living Reviews
article may evolve over
time, we recommend to cite the article as follows:
Hubert F. M. Goenner,
"On the History of Unified Field Theories",
Living Rev. Relativity 7, (2004), 2.
[Online article]: cited [<date>]
http://www.livingreviews.org/lrr-2004-2
The date in 'cited [<date>]'
then uniquely identifies the version of the article you are
referring to.