Am I right in thinking that prior to gluing, each pair of snails would have to have touched? How much touching would be necessary to establish the telepathic link? I'm interested in the degree of snail frottage required here. And what is the adjective for things snail-related?
The pasilalinic-sympathetic compass, also referred to as the snail telegraph, was a contraption built to prove the belief that snails create a permanent telepathic link when they touch. The belief was developed by French occultist Jacques Toussaint Benoit and colleague Monsieur Biat-Chretien in the early to mid 19th century. The telepathic bond was theorised to have no physical limit, with communication being possible over any distance. By touching one half of the snail partnership the other will sense the contact and will itself move.
The apparatus consists of a square wooden box containing a large horizontal disc. In the disc are 24 holes, each containing a zinc dish lined with a cloth soaked in a copper sulphate solution; the cloth was held in place by a line of copper. At the bottom of each of the 24 basins is a snail, glued in place, and each associated with a different letter of the alphabet. An identical second device holds the paired snails.
To transmit a letter the operator touches one of the snails. This causes a reaction in the corresponding snail which can be read by the receiving operator.