Xah's Math Blog Archive 2011-11 to 2011-11
Old Variant Form of the Letter “s” ſ and etymology of the integral sign ∫
Klein Bottle Opener by Bathsheba
These are made by Bathsheba. You can buy it on her site, at: www.bathsheba.com.
Klein bottle is a exotic math surface that has only one side. That is, a ant crawling on the surface can get to the other side without crossing any edge. (the natural space of Klein bottle is 4th dimension. In 3-dimension, as in the picture, the ant would have to pass wall. For more about Klein bottle and a app for interactive rotation, see: Klein Bottle.)
Note: Bathsheba has also been creative in Second Life.
She has also made a Seaslug Ride. To see more pics of her Second Life creation and location to buy, see: Seaslug Ride • Flying Ammonite.
Math: ID System, Number Base vs Number of Digits