of a silicone resin block the conductor 20 passes through a hole in frame structure 17 and is compressed into contact with one of the conductors on rigid cable portion 13 by the cover plate 18 four large screws 21 clamp the cover plate 18 to the body 15 to compress between them not only the conductor 20 but also the elastomer coated frame structure 17 the electrochromic solution is hermetically sealed within the enclosed volume formed by the cover 18 the inner walls of frame structure 17 and the chip 11 having described the basic construction of the cell the frame structure 17 will now be described in more detail with reference to fig3 to 5 as can be seen from those figures the rigid part of the frame structure 17 is a metal subframe 30 of basically rectangular shape the subframe is coated over substantially its entire surface with an inert fluorocarbon elastomeric resin 31 by means of transfer moulding process the only portions not so coated are the bores 32 for receiving the clamping bolts 21 the frame structure 17 is open in the center to define a shallow chamber for holding the electrochromic solution a cross bar 33 of reduced height divides the chamber into a main.