- The following dramatisation of the Marriage of Heaven and Hell and the introductory talk were originally broadcast on BBC Radio 3. The Blake Society is grateful to the dramatiser for making this available. As with all the recordings they are available for mp3 download on the Blake Society web site at www.blakesociety.org.uk/voice.
- Klein bottle (Wikipedia)
In mathematics, the Klein bottle (/ˈklaɪn/) is an example of a non-orientable surface; that is, informally, a one-sided surface which, if traveled upon, could be followed back to the point of origin while flipping the traveler upside down. More formally, the Klein bottle is a two-dimensional manifold on which one cannot define a normal vector at each point that varies continuously over the whole manifold. Other related non-orientable surfaces include the Möbius strip and the real projective plane. While a Möbius strip is a surface with a boundary, a Klein bottle has no boundary. For comparison, a sphere is an orientable surface with no boundary.