It is shown again that it is better to describe the contribution of the partial dipole moments to the cohesion as a Keesom effect in an extended sense, as was introduced recently by Staverman. The Debije effect can be described as mainly due to the total dipole moment of the molecules. These conceptions solve several problems, which existed hitherto in the theory of the boiling points. They show why we can expect constant “TD values” for each “type” of methane derivatives i.e. constant differences between the boiling point and the London contribution to the boiling point, and they similarly predict constant “TD values” for the halogenated ethane and ethene derivatives. We can further understand, why the completely halogenated ethane and ethene derivatives do not show “TD values”, although they possess at least two partial dipole moments. A complete survey is given of all the effects, which give rise to contributions to the boiling points.