229,485. Bowles, G. M. Feb. 16, 1924. No Patent granted (Sealing fee not paid). Variable resistances. - A contact member 23 is moved over a resistance wire 7, wound on an ebonite sleeve 6 by means of an archimedean screw 11 formed by twisting a flat-sided rod, for example of square section. The pitch may be such that the movement of the contact member 23 over the resistance 7 may be effected by one complete turn of the screw. The ebonite sleeve 6 is mounted on a framework formed by two discs 1, 2 held apart by three spacing- members 3, 4, 5. The screw 11 is formed at its upper end with a plain cylindrical portion 12 passing through a bearing 13 and provided at its upper end with a knob 17. The lower end of the screw 11 engages in a depression 19 in a flat spring 18, which is depressed if the rod 11 is over-screwed. Engaging the twisted rod 11 is a U-shaped element 20, the two limbs of which are formed with holes corresponding with the cross-section of the rod 11. Riveted to the member 20 is the contact member 23, which is shaped so as to engage the spacing members 3, 4 and is bent to a U-shape at its end and formed with a depression 25 for making contact with the resistance wire 7. One end of the resistance wire 7 is connected by a screw 8 to the spacing- member 5, the other end being connected to a terminal 9. A second terminal 10 is connected to the end of the member 5.