For example, V. Meyer and E. Riecke (1888) assumed that the carbon atom is surrounded by an æthereal envelope which, in the case of isolated atoms, has a spherical shape like that supposed to be possessed by the atoms themselves. The atom in the core carries the specific affinities; the æthereal envelope is the seat of the valencies. Each valency is determined by the presence of two opposite electrical poles—called double or di‐poles—situated at the ends of a straight line which is small in comparison with the diameter of the æthereal shell. The four valencies of carbon are represented by four such di‐poles each of which is able to move freely within the æthereal shell, and to turn freely about its middle point.