D/As,

I've found it. The book is 'Bennnett College : "Electricity" '. Bennett College was a corresondence college based in Sheffield. The appropriate bit is as follows : 'Another arrangement, suitable for very large drawing-rooms, or for restaurants, halles, schoolrooms, etc is indicated in Fig 201. The whole odf the lightig is controlled by two "Twinob" switches the ha;ves of whic hare numbered 2 and 4 and 1 and 8 respectively. Therse numbers show which of the numbered circles representing lamps, or groups of lamps, are controlled by them. Thuys when the half of the No 2 swithc marekd 1 is put on, the lamp market 1 (in what we nay take to be the centre of the ceiling) is lighted. When the 2 half of No 1 switch is put on, the 2 lamps marked 2 at each end of the room are lighted up..." This is a simplified vesion of Fig 201, showing the lamp positones, but not the wiring (which is obbious!) : (8) (4) (8) (4) (8) (2) (8) (1) (8) (2) (8) (4) (8) (4) (8) " There are two ponts about this arragement that should be noted. Firstly, whichecer half or halves of the swtichs are put on, the lighting will be symmetircal. Thus one is in the centre, the twos are in line, one at each end of the room, and 1nad 2 together form a line down the centre. The fours form a square and the eights a sort of rectangle. The one anf d the fours make a start, and the one, twos, adn foues an elongated star, and so on. This arrangement of lights points ot the necessity of securing synmmetry in similar groupings. Secondly the arragment provides for no less that 15 degrees of light as tablulated below." I refuse to type out the table, everybody here knows what it will say. A 'Twinob' switch was simply 2 toggle switches on one base, with 2 actuators (Twin Knob -? 'Twinob'). Nothing electrically odd about it. I can't find a copyright dae in the book unfortunately. I would think it's pre World War 2, though. -tony