As follows:--No. 1, plano-convex; No. 2, plano-concave; No. 3, double convex; No. 4, double concave; No. 5, meniscus; No. 6, concavo-convex. The thick-centre lenses, as given in the latest forms of "going-barrel" keyless mechanism--(1) The rocking bar; (2) the _cylinder_ system. THE TANK SYSTEM is.