This was constructed of a shallow box placed in a vertical position, with metallic front and back and insulating sides.
Cavendish proved it by enclosing a metal sphere in two hemispheres of thin metal held on insulating supports.
In the form of standard coil recommended by the Berlin Reichsanstalt the coil is immersed in an insulating oil which is kept stirred by means of a small electric motor during the time of making the measurement.
Granulated cork has practically the same insulating properties as silicate cotton, and the same thicknesses may be used.
For lager-beer cellars and fermenting rooms, for bacon-curing cellars, and for similar purposes, brick walls with single or double air spaces are used, and sometimes a space filled with silicate cotton or other insulating material.
